fix(Gax): address tracing review feedback and span lifecycle fixes

[bshaffer]

Address code review feedback on #9780 (#9573) and refine span lifecycle handling:

• Normalize gRPC status codes using string constants () and map HTTP status codes in for non-gRPC errors.
• Detach the active OpenTelemetry context scope before ending the span in and , and catch in .
• Propagate (, , ) from to transports, and wrap in a / inside () so invalid endpoints do not throw when instantiating transports directly.
• Remove unused , , and the composer dependency, and clean up constants.

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