[code_coverage] Add telemetry instrumentation to coverage.py

This change introduces OpenTelemetry instrumentation to the code
coverage generation script to improve observability into its usage and
performance.

Key changes:
- Created tools/code_coverage/.vpython3 to provide opentelemetry wheels.
- Added tools/code_coverage/telemetry_utils.py as a wrapper for the
depot_tools/infra_lib/telemetry library.
  - This library handles anonymization, trace upload, and opt-out flow.
- Instrumented Main(), _CreateCoverageProfileDataForTargets(), and
_GenerateCoverageReport() in coverage.py with spans.
- Recorded contextual metadata such as build targets and output directories.

Also addresses the presubmit errors from reverted CL
https://crrev.com/c/7765211

Bug: 501180121
Change-Id: Ia3f444bea5ae08fdce9515d4e2c01e4069af19c9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7782805
Reviewed-by: Struan Shrimpton <sshrimp@google.com>
Reviewed-by: Prakhar Asthana <pasthana@google.com>
Commit-Queue: David Hinojosa <davidhinojosa@google.com>
Cr-Commit-Position: refs/heads/main@{#1632924}
NOKEYCHECK=True
GitOrigin-RevId: 63f63a21659cb7b737c64e3cff3a57fc4625f0c5