perf: improve performance of code-to-function lookups [backport 2.21] (#13400)

Backport 205fd1e from #13393 to 2.21.

We increase the LRU cache size of the function-for-code lookup to avoid
potentially excessive churn. The default size of 128 might be too small
since it is a cache on a utility function that is shared by many other
components.

## Checklist
- [x] 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](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
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[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
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- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
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[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Co-authored-by: Gabriele N. Tornetta <[email protected]>

Author: github-actions[bot]

ddtrace/internal/utils/inspection.py

@@ -126,7 +126,7 @@ def collect_code_objects(code: CodeType) -> Iterator[CodeType]:
             q.append(new_code)
 
 
-@lru_cache()
+@lru_cache(maxsize=(1 << 14))  # 16k entries
 def functions_for_code(code: CodeType) -> List[FunctionType]:
     import gc
 

releasenotes/notes/prf-functions_for_code-9634ef79190978cf.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    code origin for spans: fixes a performance issue with exit spans.