[Souheyl7Gouadria]

Don't expire infinite Kestrel timeouts on the next heartbeat

Make Timeout.InfiniteTimeSpan actually disable KeepAliveTimeout and RequestHeadersTimeout.

Description

KestrelServerLimits stores an infinite timeout as TimeSpan.MaxValue, which ToTicks turns into long.MaxValue. TimeoutControl.AssignTimeout then adds the last timestamp and the heartbeat interval to it. The sum wraps negative and the timeout fires on the next heartbeat. So an idle connection with an infinite keep-alive closes after about a second, and incomplete headers with an infinite header timeout get a 408. HTTP/2 goes through the same code.

The expiration is now clamped to long.MaxValue on overflow, the same way Http3Connection already handles its stream timeouts.

Added a TimeoutControl test and functional tests for both limits.

Fixes #69692

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[dotnet-policy-service]

Thanks for your PR, @Souheyl7Gouadria. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

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