Add Datadog code coverage upload

[ManuelPalenzuelaDD]

What does this PR do?

We're migrating Datadog repositories 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/coverage-upload-github-action@v1 step after the existing Codecov upload in the dev.yml workflow test job
• Uses DD_API_KEY_CI_APP secret (already available in the repo for CI Visibility)
• Coverage format: LCOV (generated by llvm-cov export)
• The existing Codecov uploads are unchanged — nothing is removed or modified
• The upload uses continue-on-error: 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 — dev.yml triggers on push only (not PRs), so the Datadog upload will run after merge.

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.