Add Datadog code coverage upload

[ManuelPalenzuelaDD]

What does this PR do?

We're migrating Datadog repos from Codecov to Datadog Code Coverage for tracking test coverage. This PR is the first step: it adds a Datadog coverage upload alongside the existing Codecov upload so we can run both systems in parallel and verify parity before switching over.

Changes

• Added datadog-ci coverage upload step to the GitLab CI coverage job, immediately after the existing Codecov upload
• Coverage format: LCOV (generated by llvm-cov export)
• The existing Codecov uploads are unchanged — nothing is removed or modified
• The upload uses || true so it cannot block CI

Why are we doing this?

As part of a company-wide effort, we're consolidating code coverage reporting into Datadog's own Code Coverage product. This gives us:

• Coverage data integrated directly into Datadog CI Visibility
• PR gates and coverage checks natively in Datadog
• No dependency on a third-party service (Codecov) for coverage reporting

Validation

Pending — CI will run with secrets now that this PR is from origin.

Next steps (not in this PR)

Once this PR is merged and we've confirmed Datadog coverage is stable over several commits:

1. Remove the Codecov upload steps and CODECOV_TOKEN secret
2. Optionally configure PR gates in code-coverage.datadog.yml

No action needed from reviewers beyond normal review

This is a low-risk, additive change. The new upload step runs independently of the existing CI pipeline and cannot cause test failures.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.85%. Comparing base (69b4e6d) to head (6d82935).
⚠️ Report is 9 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #337   +/-   ##
=======================================
  Coverage   68.85%   68.85%           
=======================================
  Files          56       56           
  Lines        7471     7471           
  Branches     1058     1058           
=======================================
  Hits         5144     5144           
  Misses       1820     1820           
  Partials      507      507           

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[ManuelPalenzuelaDD]

Superseded by #339 — fresh branch from master to fix Vault permissions issue.