feat: add non-mutating set_scalar_constants

[MilesCranmerBot]

This adds a non-mutating set_scalar_constants helper that returns a new tree with updated scalar constants.

Motivation (empirical): trying to run ForwardDiff.gradient through set_scalar_constants! on a Node{Float64} fails because constant node fields are concretely typed (e.g. cannot assign Dual into Float64). The new helper promotes the tree number type to accommodate eltype(constants) (so Duals work), sets the constants, and returns the new tree.

Changes:

• Add set_scalar_constants(tree, constants) (non-mutating; promotes number type if needed).
• Add set_scalar_constants(ex::Expression, constants) wrapper.
• Add a regression test demonstrating ForwardDiff gradients w.r.t. constants.

Tests:

• Pkg.test()

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 59.59%. Comparing base (efbc2aa) to head (b2ef7fc).

Files with missing lines	Patch %	Lines
src/NodeUtils.jl	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #165      +/-   ##
==========================================
+ Coverage   59.43%   59.59%   +0.16%     
==========================================
  Files          30       30              
  Lines        2682     2693      +11     
==========================================
+ Hits         1594     1605      +11     
  Misses       1088     1088              

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[github-actions]

Benchmark Results (Julia v1)

Time benchmarks

	master	b2ef7fc...	master / b2ef7fc...
eval/ComplexF32/evaluation	6.92 ± 0.49 ms	6.92 ± 0.53 ms	1 ± 0.1
eval/ComplexF64/evaluation	10.2 ± 0.79 ms	10.3 ± 0.86 ms	0.991 ± 0.11
eval/Float32/derivative	11.1 ± 1.5 ms	11.2 ± 0.9 ms	0.996 ± 0.16
eval/Float32/derivative_turbo	11.1 ± 1.7 ms	11.2 ± 1.3 ms	0.99 ± 0.19
eval/Float32/evaluation	2.46 ± 0.26 ms	2.46 ± 0.25 ms	1 ± 0.14
eval/Float32/evaluation_bumper	0.604 ± 0.016 ms	0.575 ± 0.017 ms	1.05 ± 0.042
eval/Float32/evaluation_turbo	0.533 ± 0.04 ms	0.527 ± 0.038 ms	1.01 ± 0.11
eval/Float32/evaluation_turbo_bumper	0.602 ± 0.017 ms	0.57 ± 0.016 ms	1.05 ± 0.041
eval/Float64/derivative	14.6 ± 2.8 ms	14.3 ± 3.9 ms	1.02 ± 0.34
eval/Float64/derivative_turbo	14.4 ± 2.9 ms	14.2 ± 3 ms	1.01 ± 0.29
eval/Float64/evaluation	2.88 ± 0.29 ms	2.88 ± 0.31 ms	0.998 ± 0.15
eval/Float64/evaluation_bumper	1.27 ± 0.046 ms	1.2 ± 0.048 ms	1.06 ± 0.058
eval/Float64/evaluation_turbo	1.03 ± 0.069 ms	1.02 ± 0.064 ms	1.01 ± 0.092
eval/Float64/evaluation_turbo_bumper	1.27 ± 0.044 ms	1.2 ± 0.049 ms	1.06 ± 0.057
utils/combine_operators/break_sharing	0.0421 ± 0.0015 ms	0.0409 ± 0.0011 ms	1.03 ± 0.045
utils/convert/break_sharing	27.7 ± 3.6 μs	27.4 ± 3.3 μs	1.01 ± 0.18
utils/convert/preserve_sharing	0.0977 ± 0.0082 ms	0.0988 ± 0.009 ms	0.988 ± 0.12
utils/copy/break_sharing	28.1 ± 3.8 μs	27.6 ± 3.4 μs	1.02 ± 0.19
utils/copy/preserve_sharing	0.099 ± 0.0094 ms	0.0991 ± 0.01 ms	0.999 ± 0.14
utils/count_constant_nodes/break_sharing	12.7 ± 0.83 μs	12.5 ± 1 μs	1.02 ± 0.11
utils/count_constant_nodes/preserve_sharing	0.0841 ± 0.0055 ms	0.085 ± 0.0065 ms	0.989 ± 0.099
utils/count_depth/break_sharing	14.5 ± 1.1 μs	13.5 ± 1 μs	1.07 ± 0.12
utils/count_nodes/break_sharing	12.5 ± 0.73 μs	12.2 ± 0.85 μs	1.02 ± 0.093
utils/count_nodes/preserve_sharing	0.0855 ± 0.0061 ms	0.0873 ± 0.0064 ms	0.98 ± 0.1
utils/get_set_constants!/break_sharing	0.0328 ± 0.0034 ms	0.0332 ± 0.0039 ms	0.989 ± 0.16
utils/get_set_constants!/preserve_sharing	0.173 ± 0.011 ms	0.172 ± 0.012 ms	1 ± 0.093
utils/get_set_constants_parametric	0.045 ± 0.0047 ms	0.0459 ± 0.0045 ms	0.98 ± 0.14
utils/has_constants/break_sharing	7.58 ± 1 μs	7.75 ± 1.4 μs	0.979 ± 0.22
utils/has_operators/break_sharing	2.67 ± 0.26 μs	2.54 ± 0.14 μs	1.05 ± 0.12
utils/hash/break_sharing	24.2 ± 1.8 μs	23.6 ± 1.5 μs	1.03 ± 0.1
utils/hash/preserve_sharing	0.0988 ± 0.0059 ms	0.101 ± 0.0088 ms	0.975 ± 0.1
utils/index_constant_nodes/break_sharing	29.2 ± 2.1 μs	28.6 ± 2.4 μs	1.02 ± 0.11
utils/index_constant_nodes/preserve_sharing	0.0995 ± 0.0049 ms	0.102 ± 0.0079 ms	0.98 ± 0.09
utils/is_constant/break_sharing	8.47 ± 1.3 μs	8.02 ± 1 μs	1.06 ± 0.22
utils/simplify_tree/break_sharing	31.2 ± 1.3 μs	30.7 ± 1.4 μs	1.02 ± 0.064
utils/simplify_tree/preserve_sharing	0.112 ± 0.0064 ms	0.112 ± 0.007 ms	0.999 ± 0.085
utils/string_tree/break_sharing	0.443 ± 0.026 ms	0.434 ± 0.02 ms	1.02 ± 0.075
utils/string_tree/preserve_sharing	0.532 ± 0.02 ms	0.535 ± 0.021 ms	0.995 ± 0.054
time_to_load	0.168 ± 0.0021 s	0.172 ± 0.006 s	0.978 ± 0.036

Memory benchmarks

	master	b2ef7fc...	master / b2ef7fc...
eval/ComplexF32/evaluation	0.987 k allocs: 2.53 MB	0.96 k allocs: 2.46 MB	1.03
eval/ComplexF64/evaluation	0.975 k allocs: 4.97 MB	0.987 k allocs: 5.03 MB	0.988
eval/Float32/derivative	4.55 k allocs: 17.1 MB	4.68 k allocs: 17.6 MB	0.972
eval/Float32/derivative_turbo	4.67 k allocs: 17.6 MB	4.66 k allocs: 17.5 MB	1
eval/Float32/evaluation	0.987 k allocs: 1.29 MB	0.987 k allocs: 1.29 MB	1
eval/Float32/evaluation_bumper	0.303 k allocs: 0.393 MB	0.303 k allocs: 0.393 MB	1
eval/Float32/evaluation_turbo	0.966 k allocs: 1.26 MB	0.969 k allocs: 1.26 MB	0.997
eval/Float32/evaluation_turbo_bumper	0.303 k allocs: 0.393 MB	0.303 k allocs: 0.393 MB	1
eval/Float64/derivative	4.77 k allocs: 0.0349 GB	4.83 k allocs: 0.0353 GB	0.987
eval/Float64/derivative_turbo	4.77 k allocs: 0.0349 GB	4.8 k allocs: 0.0351 GB	0.992
eval/Float64/evaluation	1.01 k allocs: 2.58 MB	0.999 k allocs: 2.56 MB	1.01
eval/Float64/evaluation_bumper	0.303 k allocs: 0.771 MB	0.303 k allocs: 0.771 MB	1
eval/Float64/evaluation_turbo	0.99 k allocs: 2.53 MB	0.975 k allocs: 2.5 MB	1.02
eval/Float64/evaluation_turbo_bumper	0.303 k allocs: 0.771 MB	0.303 k allocs: 0.771 MB	1
utils/combine_operators/break_sharing	4 allocs: 0.953 kB	4 allocs: 0.953 kB	1
utils/convert/break_sharing	2 k allocs: 0.123 MB	2 k allocs: 0.123 MB	1
utils/convert/preserve_sharing	2.4 k allocs: 0.192 MB	2.4 k allocs: 0.192 MB	1
utils/copy/break_sharing	2 k allocs: 0.123 MB	2 k allocs: 0.123 MB	1
utils/copy/preserve_sharing	2.4 k allocs: 0.192 MB	2.4 k allocs: 0.192 MB	1
utils/count_constant_nodes/break_sharing	4 allocs: 0.953 kB	4 allocs: 0.953 kB	1
utils/count_constant_nodes/preserve_sharing	0.404 k allocs: 0.0696 MB	0.404 k allocs: 0.0696 MB	1
utils/count_depth/break_sharing	4 allocs: 0.953 kB	4 allocs: 0.953 kB	1
utils/count_nodes/break_sharing	4 allocs: 0.953 kB	4 allocs: 0.953 kB	1
utils/count_nodes/preserve_sharing	0.404 k allocs: 0.0696 MB	0.404 k allocs: 0.0696 MB	1
utils/get_set_constants!/break_sharing	0.898 k allocs: 25.2 kB	0.898 k allocs: 25.2 kB	1
utils/get_set_constants!/preserve_sharing	1.7 k allocs: 0.138 MB	1.7 k allocs: 0.138 MB	1
utils/get_set_constants_parametric	1.42 k allocs: 0.0663 MB	1.42 k allocs: 0.0663 MB	1
utils/has_constants/break_sharing	4 allocs: 0.203 kB	4 allocs: 0.203 kB	1
utils/has_operators/break_sharing	4 allocs: 0.203 kB	4 allocs: 0.203 kB	1
utils/hash/break_sharing	0.104 k allocs: 2.52 kB	0.104 k allocs: 2.52 kB	1
utils/hash/preserve_sharing	0.504 k allocs: 0.0711 MB	0.504 k allocs: 0.0711 MB	1
utils/index_constant_nodes/break_sharing	2.1 k allocs: 0.094 MB	2.1 k allocs: 0.094 MB	1
utils/index_constant_nodes/preserve_sharing	2.5 k allocs: 0.163 MB	2.5 k allocs: 0.163 MB	1
utils/is_constant/break_sharing	4 allocs: 0.203 kB	4 allocs: 0.203 kB	1
utils/simplify_tree/break_sharing	0.104 k allocs: 2.52 kB	0.104 k allocs: 2.52 kB	1
utils/simplify_tree/preserve_sharing	0.504 k allocs: 0.0711 MB	0.504 k allocs: 0.0711 MB	1
utils/string_tree/break_sharing	11.9 k allocs: 0.999 MB	11.9 k allocs: 0.999 MB	1
utils/string_tree/preserve_sharing	12.3 k allocs: 1.07 MB	12.3 k allocs: 1.07 MB	1
time_to_load	0.145 k allocs: 11 kB	0.145 k allocs: 11 kB	1