Produce different keys for inline ratelimiting policies

[Youssef1313]

Fixes #67326

[Copilot]

Pull request overview

This PR fixes a rate-limiting correctness issue where inline RequireRateLimiting(IRateLimiterPolicy<T>) policies could unintentionally share cached limiters when they produced equal partition keys, causing cross-policy collisions and incorrect limiter configuration being applied.

Changes:

• Namespaces inline policy partition keys so distinct inline policy instances no longer collide when producing equal partition keys.
• Adds tests verifying (1) two different inline policy instances don’t share a limiter for the same key, and (2) the same policy instance reused across endpoints still shares.
• Introduces a small stateful test RateLimiter/policy to observe limiter sharing vs isolation behavior.

Reviewed changes

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

File	Description
src/Middleware/RateLimiting/src/RateLimiterEndpointConventionBuilderExtensions.cs	Adds a per-inline-policy namespace token to avoid cross-policy partition collisions.
src/Middleware/RateLimiting/test/RateLimitingMiddlewareTests.cs	Adds regression tests and a small counting limiter/policy to validate isolation vs sharing behavior.

Suppressed comments (1)

src/Middleware/RateLimiting/test/RateLimitingMiddlewareTests.cs:740

• CountingRateLimiter.GetStatistics returns null even though the overridden return type is non-nullable. This can produce nullable warnings and may break the build if warnings are treated as errors. Prefer throwing NotImplementedException (consistent with other test limiters) since the test doesn't use statistics.

        public override RateLimiterStatistics GetStatistics() => null;

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