Add timeout error classification

[SamRemis]

This pull request centralizes and clarifies timeout handling across the async client and transport layers by adding a transport-level error classification API and surfacing transport-detected timeouts as a dedicated ClientTimeoutError. Transports now return an ErrorInfo that indicates whether an exception represents a timeout and whether the fault is client- or server-side, and the core async client consults that information and raises ClientTimeoutError when appropriate so callers see a single, consistent exception for client-side timeouts.

ClientTransport implementations must now implement get_error_info(exception, **kwargs) and return an ErrorInfo indicating whether the exception is a timeout and whether the fault is client- or server-side. The break was required so the core async client can reliably classify transport errors and raise a single ClientTimeoutError for client-side timeouts. This information is necessary for handling errors as a part of retries.