build: remove rust-version from private crates

[xtqqczze]

We don't publish num-prime-bench, it doesn't need rust-version.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.04%. Comparing base (3f5db7d) to head (cfae92b).
⚠️ Report is 77 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #129      +/-   ##
==========================================
+ Coverage   78.64%   86.04%   +7.39%     
==========================================
  Files          13       16       +3     
  Lines        2585     3933    +1348     
  Branches      230      265      +35     
==========================================
+ Hits         2033     3384    +1351     
+ Misses        552      546       -6     
- Partials        0        3       +3     

Flag	Coverage Δ
macos_latest	85.99% <ø> (+8.35%)	⬆️
ubuntu_latest	85.60% <ø> (+7.42%)	⬆️
windows_latest	15.40% <ø> (+0.70%)	⬆️

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[codspeed]

Merging this PR will improve performance by 22.36%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 2 improved benchmarks
✅ 22 untouched benchmarks
⏩ 9 skipped benchmarks¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	three 39-bit primes (u128)	480.2 ms	360.9 ms	+33.06%
⚡	five 38-bit primes (191 bits)	2 s	1.8 s	+12.53%

Tip

Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing xtqqczze:private-rust-version (cfae92b) with main (866bc2c)}

Footnotes

1. 9 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩