chore: [SVLS-5265] add span links to encoded spans

[apiarian-datadog]

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/internal/encoding.py                                            @DataDog/apm-core-python
tests/integration/test_encoding.py                                      @DataDog/apm-core-python
tests/tracer/test_encoders.py                                           @DataDog/apm-sdk-api-python

[apiarian-datadog]

followup from DataDog/datadog-lambda-python#513 where we are using the logwriter output and missing the span links for our integration tests.

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: aleksandr.pasechnik/svls-5265-span-links-serialized-logwriter
Commit report: 71d512b
Test service: dd-trace-py

✅ 0 Failed, 1129 Passed, 157 Skipped, 26m 42.18s Total duration (9m 41s time saved)

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-10-08 18:23:59

Comparing candidate commit 71d512b in PR branch aleksandr.pasechnik/svls-5265-span-links-serialized-logwriter with baseline commit cd1753d in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 371 metrics, 53 unstable metrics.