Improve Polly coverage

[martincostello]

Extend coverage for unit tests and mutations with low-hanging-fruit parameter validation and removing redundant code.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.42%. Comparing base (6a617ed) to head (9bc74ea).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2505      +/-   ##
==========================================
+ Coverage   85.36%   86.42%   +1.05%     
==========================================
  Files         312      312              
  Lines        7468     7468              
  Branches     1121     1091      -30     
==========================================
+ Hits         6375     6454      +79     
+ Misses        908      852      -56     
+ Partials      185      162      -23     

Flag	Coverage Δ
linux	86.42% <100.00%> (+1.05%)	⬆️
macos	86.42% <100.00%> (+1.05%)	⬆️
windows	86.38% <100.00%> (+1.06%)	⬆️

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[Copilot]

Copilot reviewed 30 out of 41 changed files in this pull request and generated 2 comments.

Files not reviewed (11)

• src/Polly/Polly.csproj: Language not supported
• src/Polly/RateLimit/LockFreeTokenBucketRateLimiter.cs: Evaluated as low risk
• src/Polly/Retry/AsyncRetryPolicy.cs: Evaluated as low risk
• src/Polly/Timeout/AsyncTimeoutPolicy.cs: Evaluated as low risk
• src/Polly/Retry/RetryPolicy.cs: Evaluated as low risk
• src/Polly/Bulkhead/BulkheadPolicy.cs: Evaluated as low risk
• src/Polly/Timeout/TimeoutPolicy.cs: Evaluated as low risk
• src/Polly/Bulkhead/AsyncBulkheadPolicy.cs: Evaluated as low risk
• src/Polly/Fallback/AsyncFallbackPolicy.cs: Evaluated as low risk
• src/Polly/Fallback/FallbackPolicy.cs: Evaluated as low risk
• src/Polly/RateLimit/RateLimitPolicy.cs: Evaluated as low risk

Comments suppressed due to low confidence (1)

src/Polly/RateLimit/AsyncRateLimitPolicy.cs:50

• The null check for 'rateLimiter' was removed. This can lead to a potential null reference exception if 'rateLimiter' is null.

_rateLimiter = rateLimiter;