feat(auth): enrich invoke-level telemetry with transport detail

[westarle]

This PR has auth code fill in TelemetryTransportData in order to send details from the transport back up to higher layers. See googleapis/gax-go#496. This in turn allows code in those higher layers to report telemetry information for the last request that is only known by the transport layer.

Changes Made

• Logical Hostname Extraction: Updated extraction logic to parse logical hostnames and ports directly from req.URL (HTTP) and cc.Target() (gRPC) prior to invoking the transport
  layer.
• Implicit Port Fallback: Added scheme-based port fallbacks (80 for HTTP, 443 for HTTPS) when handling URLs with implicit ports.

[gemini-code-assist]

Code Review

This pull request enhances OpenTelemetry integration by adding metrics support for both gRPC and HTTP transports. For gRPC, a new unary client interceptor is introduced to extract server address and port from the target and populate gax.TransportTelemetryData, utilizing a new extractHostPort helper function. For HTTP, the otelAttributeTransport is updated to similarly extract server address, port, and response status code. New unit tests cover these telemetry functionalities and the extractHostPort helper. Review feedback indicates an improvement opportunity in extractHostPort's error handling when the port is invalid, suggesting it should return the parsed host instead of the full target string, along with a corresponding test case update.