In this PR:

• Service Identity Attributes (Phase 1): Updated NewClient (gRPC) and NewRESTClient (HTTP) generation to include gcp.client.version (via getVersionClient()) and gcp.client.repo ("googleapis/google-cloud-go") in the WithTelemetryAttributes internal option.
• AIP-Compliant Resource Identification (Phase 2a): Implemented a resourceNameField helper that scans request fields for the google.api.resource_reference annotation, including tie-breaking logic that prioritizes fields appearing in the HTTP path pattern.
• Canonical Prefixing: Updated resource name injection to prepend the Service Data Host (e.g., fmt.Sprintf("//service.host/%v", req.GetResourceNameField())).
• REST Span Renaming: Updated REST method generation to inject the url.template metadata key containing the raw HTTP path pattern.
• Test Verification: Updated gengapic_test.go and genrest_test.go fixtures to include resource_reference and default_host, and regenerated all golden files.
• Tracing Allow-listing: Add a gated feature to gate tracing to a strictly defined list of services (test canaries, early adopters).

Missing from this PR:

Heuristic Logic

• Vocabulary Learning: Implement logic to scan service definitions at generation-time and build a vocabulary of valid resource types (e.g., projects, instances, buckets) from literals in HTTP path patterns.
• Path Reconstruction: Implement logic to parse "exploded" HTTP paths and generate code to reassemble multiple request fields into a single "Canonical Relative Resource Name."
• Path Pruning: Enhance the path parser to identify and prune non-resource segments (e.g., custom verbs like :access or sub-resource actions) from the end of the reconstructed name.
• Heuristic Logic Allow-listing: Add a configuration mechanism to gate this advanced heuristic logic to a strictly defined list of legacy services (Compute Engine, Cloud SQL, BigQuery).