RateLimiting: add typed builder/guard tests and external limiter lifetime test

[mohammed-saalim]

The issue or feature being addressed

Add small, focused unit tests for RateLimiting to increase coverage. No product code changes.

Details on the issue fix or feature implementation

• Typed builder:
  • ResiliencePipelineBuilder<int>().AddConcurrencyLimiter(...).Build() produces RateLimiterResilienceStrategy.
• Guard/validation:
  • Null limiter/options throw ArgumentNullException.
  • Invalid options (null DefaultRateLimiterOptions) throw ValidationException.
• Lifetime:
  • External RateLimiter passed to .AddRateLimiter(limiter) is NOT disposed when a ResiliencePipelineRegistry is disposed.

Files added

• test/Polly.RateLimiting.Tests/RateLimiterResiliencePipelineBuilderExtensions_TypedAndNullTests.cs
• test/Polly.RateLimiting.Tests/RateLimiterExternalLimiterLifetimeTests.cs

Notes

• No changes to product code or central package versions.
• All target frameworks passed locally (net9.0, net8.0, net481).

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature
• I have successfully run a local build

[martincostello]

What missing coverage is this change adding exactly? The code coverage score is 100% for the library and it also has a mutation score of 100.

Those number suggest there's no missing tests.

[mohammed-saalim]

@martincostello Thanks for the review! You’re right that coverage and mutation scores are already 100%. These tests aren’t to raise the percentage, but to lock in a few behavioral contracts:
External limiter lifetime: when a user passes a limiter into AddRateLimiter(limiter), disposing a ResiliencePipelineRegistry should not dispose that external limiter. This scenario wasn’t explicitly covered.
Typed builder wiring: ResiliencePipelineBuilder().AddConcurrencyLimiter(...) composes a RateLimiterResilienceStrategy for typed pipelines. This typed path wasn’t asserted.
Null-argument guards: explicit ArgumentNullException checks for the builder extension overloads (minor clarity; I can drop if you prefer).
If you’d like, I can fold these into the existing RateLimiterResiliencePipelineBuilderExtensionsTests and remove anything you consider redundant. Happy to keep only the external-limiter lifetime and typed-builder wiring tests if that’s your preference.

[mohammed-saalim]

Moved the tests into RateLimiterResiliencePipelineBuilderExtensionsTests.cs as requested and removed the two standalone files. All TFMs pass locally (net9.0, net8.0, net481). Ready for another look. See PR #2711. @martincostello

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.12%. Comparing base (f52f37f) to head (476818d).
⚠️ Report is 26 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2711      +/-   ##
==========================================
- Coverage   96.23%   96.12%   -0.11%     
==========================================
  Files         311      309       -2     
  Lines        7322     7118     -204     
  Branches     1012     1008       -4     
==========================================
- Hits         7046     6842     -204     
  Misses        222      222              
  Partials       54       54              

Flag	Coverage Δ
linux	96.12% <ø> (-0.11%)	⬇️
macos	96.12% <ø> (-0.11%)	⬇️
windows	96.11% <ø> (-0.11%)	⬇️

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[martincostello]

Thanks!