feat(nvca): add OTel semconv metrics for outbound dependency clients (3.1)

[rohithb-hub]

TL;DR

Backport of #583 to the NVCA 3.1 release line. Cherry-picks the squash-merged
mainline commit onto release-src/compute-plane-services/nvca/v3.1.

Additional Details

Instruments NVCA outbound dependency calls with OpenTelemetry Semantic Conventions
metrics bridged to the existing Prometheus /metrics endpoint. Everything is gated
by the ClientMetrics feature flag, off by default, so this is a no-op on 3.1
unless the flag is explicitly enabled.

Cherry-pick applied with one conflict: the root MODULE.bazel use_repo line
differed because main has accumulated unrelated Bazel deps since 3.1 branched. The
3.1 version was kept — it already contains all the OTel Bazel entries this commit
needs (io_opentelemetry_go_otel_exporters_prometheus, io_opentelemetry_go_otel_sdk_metric).
All source and vendor changes applied without conflict.

For the Reviewer

Compare this diff with #583. The only intentional deviation from the mainline commit
is the MODULE.bazel use_repo line, which retains the 3.1 state rather than
pulling in unrelated main-branch Bazel deps.

For QA

No QA needed. The ClientMetrics flag is off by default. With it off the pipeline
installs a no-op meter provider and all decorators return the inner client unchanged,
identical to the behaviour before this change.

Ran focused Go tests on the 3.1 branch:

go test ./internal/metrics/... ./internal/otel/... ./pkg/nvca/... \
  -ldflags '-X github.com/NVIDIA/k8s-dra-driver-gpu/internal/info.version=v25.8.0' \
  -count=1

Issues

NO-REF

Backport of #583

Checklist

• I am familiar with the Contributing Guidelines.
• I have signed off my commits for Developer Certificate of Origin (DCO) compliance.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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