fix: rm functions_for_code usage in code origins [backport 2.21]

[github-actions]

Backport a6520bc from #13539 to 2.21.

Remove the call to functions_for_code from code origins. For Python3.11+ we'll use the fully qualified name stored on the Code Object:

https://docs.python.org/3/reference/datamodel.html#codeobject.co_qualname

For older version, we'll fall back to the function name.

refs: DEBUG-3967

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

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-06-02 19:22:09

Comparing candidate commit 36c5570 in PR branch backport-13539-to-2.21 with baseline commit 64d6eb7 in branch 2.21.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 344 metrics, 2 unstable metrics.

[github-actions]

CODEOWNERS have been resolved as:

releasenotes/notes/fix-co-performance-4199f97341fa4aa7.yaml             @DataDog/apm-python
ddtrace/debugging/_origin/span.py                                       @DataDog/debugger-python