feat(ds): add map mutation helpers

[simPod]

Adds Java-style Ds\Map mutation helpers: mapPutIfAbsent(), mapCompute(), mapComputeIfAbsent(), and mapComputeIfPresent().

The compute helpers mutate the provided map and use null computed values for the Java-style remove/do-not-add semantics.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.42857% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.13%. Comparing base (748039d) to head (c90043e).
⚠️ Report is 2 commits behind head on 0.2.x.

Files with missing lines	Patch %	Lines
src/functions_include.php	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            0.2.x      #88      +/-   ##
==========================================
+ Coverage   85.93%   89.13%   +3.19%     
==========================================
  Files           6        7       +1     
  Lines          64       92      +28     
==========================================
+ Hits           55       82      +27     
- Misses          9       10       +1     

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