impl(gax-internal): integrate RequestRecorder with gRPC transport for Server Streaming

[haphungw]

Extend RequestRecorder into the server streaming implementation in gaxi. This ensures that transport-level metrics and spans are captured for server streams.

Note:
TODO (#5372): the span created by WithTransportSpan only covers stream initiation, and we should consider instrumenting the returned stream to capture errors during the stream's lifetime.

[codecov]

Codecov Report

❌ Patch coverage is 97.36842% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 97.60%. Comparing base (0d5080d) to head (efce3cf).

Files with missing lines	Patch %	Lines
src/gax-internal/src/grpc.rs	97.36%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5375      +/-   ##
==========================================
+ Coverage   97.58%   97.60%   +0.01%     
==========================================
  Files         222      222              
  Lines       46609    46625      +16     
==========================================
+ Hits        45485    45506      +21     
+ Misses       1124     1119       -5     

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[suzmue]

Suggested change

	if _prior_attempt_count > 0 {
	Some(_prior_attempt_count)
	} else {
	None
	(_prior_attempt_count > 0).then_some(_prior_attempt_count)

[suzmue]

Suggested change

	let (service, version, repo, artifact) = if let Some(info) = attrs.instrumentation {
	(
	Some(info.service_name),
	Some(info.client_version),
	Some("googleapis/google-cloud-rust"),
	Some(info.client_artifact),
	)
	} else {
	(None, None, None, None)
	};
	let (service, version, repo, artifact) = attrs.instrumentation
	.map(|info| (
	Some(info.service_name),
	Some(info.client_version),
	Some("googleapis/google-cloud-rust"),
	Some(info.client_artifact),
	))
	.unwrap_or_default();

[suzmue]

(no action on this pr), it might be nice to add some helpers that allow us to chain these more easily so the code can look like

let pending = pending
  .with_transport_metric(self.metric.clone(), 0)
  .with_transport_logging()
  .with_transport_spane(span);