Add test to verify that _dd.span_links span_id is zero-padded to 16 hex chars

[mcculls]

Motivation

Relevant section of the RFC: https://docs.google.com/document/d/1RcTjO8ER5FNweJ0rqVcQEbf6tb1PrlPsQ6coZZww8Xg/edit?tab=t.0#heading=h.pwna8rp9exnf

Current test checks linking to a random span-id, which may or may not need padding. The new test uses a span-id that will definitely require padding.

Changes

Add test to specifically verify that _dd.span_links span_id is zero-padded to 16 hex chars

Workflow

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   • Test logic is modified? -> Get a review from RFC owner.
   • Framework is modified, or non obvious usage of it -> get a review from R&P team

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Reviewer checklist

• Anything but tests/ or manifests/ is modified ? I have the approval from R&P team
• A docker base image is modified?
  • the relevant build-XXX-image label is present
• A scenario is added, removed or renamed?
  • Get a review from R&P team

[github-actions]

CODEOWNERS have been resolved as:

manifests/cpp.yml                                                       @DataDog/system-tests-reviewers
manifests/nodejs.yml                                                    @DataDog/system-tests-reviewers
manifests/ruby.yml                                                      @DataDog/system-tests-reviewers
tests/parametric/test_span_links.py                                     @DataDog/system-tests-core @DataDog/apm-sdk-capabilities

[datadog-datadog-prod-us1]

✅ All CI checks and tests passed.

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

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[chatgpt-codex-connector]

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