## What changed
- Record `exec_server_client_requests_total` for every client RPC call attempt,
labeled by protocol method.
- Count attempts before local admission so rejected, timed-out, cancelled, and
transport-failed calls are included, while notifications and responses are not.
- Export the counter to configured OpenTelemetry collectors while excluding it
from the built-in Statsig metrics set.
## Testing
- Cover every RPC call entry point, successful responses, local and transport
failures, timeouts, cancellation, notifications, and disabled metrics.
- Verify that the OTLP HTTP exporter retains the counter.
GitOrigin-RevId: d266e840d5871aa2c34bed8ce44f3345e2b4650f
