stabilize geometric inverse cdf and clean lint warnings

[day01]

Summary

• Stabilize Geometric::inverse_cdf with a closed-form implementation to avoid platform-dependent bisection drift (Windows/no_std failure).
• Remove unused testing_boiler imports that caused -Dwarnings failures in coverage/nightly.

Testing

• cargo fmt -- --check
• cargo clippy --all-targets (remaining warnings only in kernel tests: uninlined_format_args, unchanged)
• (to run in CI) cargo test --no-default-features -F rand --target x86_64-pc-windows-gnu or windows-latest and cargo +nightly llvm-cov --no-report nextest

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 94.40%. Comparing base (5da3470) to head (a09585c).
⚠️ Report is 10 commits behind head on master.

Files with missing lines	Patch %	Lines
src/distribution/geometric.rs	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #364      +/-   ##
==========================================
- Coverage   94.99%   94.40%   -0.60%     
==========================================
  Files          61       59       -2     
  Lines       13615    12963     -652     
==========================================
- Hits        12934    12238     -696     
- Misses        681      725      +44     

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[day01]

@YeungOnion added tests and some lint fixes