[release/11.0] Add SequenceReaderExtensions.TryPeekEndian

[github-actions]

Customer Impact

• Customer reported
• Found internally

Adds the SequenceReader<byte>TryPeekLittleEndian and TryPeekBigEndian extension methods, allowing callers to inspect numeric values without advancing the reader. This addresses customer demand captured in API proposal #116414 and backports the API addition from #130178. It is not strictly associated with other .NET 11 features, and does not change existing behavior.

Regression

• Yes
• No

Testing

The API and behavior are covered by the tests included in #130178. The tests verify little-endian and big-endian peeking, including insufficient data, and that peeking does not advance the reader.

Risk

Low. This adds new API surface area on top of what is included in RC1, but it is a focused, additive API with isolated implementation and tests. It does not alter existing APIs or behavior. Other endian-aware SequenceReader APIs remain outside the scope of this backport.

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[jeffhandley]

/ba-g Failures are System.Net.Tests.InvalidClientRequestTests.GetContext_InvalidRequest_DoesNotGetContext times out (#132336)

[jeffhandley]

@artl93 This does not strictly meet the bar, so I was on the fence for bringing it for consideration. The standalone aspect and tangential relation to other feature areas made me want to run it by you for consideration.

[artl93]

@jeffhandley - I'm struggling with this one too - the timing is unfortunate, since we're locking down. This doesn't strike me as a quality or scenario completeness improvement based on the description or the API request. Is there more context?

[jeffhandley]

@artl93 -- Thanks for considering it. I thought it was worth consideration since it's in the same spirit of some other work in .NET 11 even though it's not directly related, but we can reject this one and let it get introduced in .NET 12.

/cc @tannergooding