fix(tracer): improve error handling for subprocess instrumentation [backport 3.9] (#13702)

Backport cb08856 from #13625 to 3.9.

This PR improves error handling for subprocess instrumentation. This PR
fixes #13208

**Restructured error handling**: Moved subprocess calls outside of
try-except blocks so legitimate errors are properly propagated:
  ```python
  # After (CORRECT - preserves errors)
  @trace_utils.with_traced_module  
def _traced_subprocess_init(module, pin, wrapped, instance, args,
kwargs):
      if not should_instrument:
          return wrapped(*args, **kwargs)
      
      try:
          # Only tracing logic in try-catch, not the subprocess call
          # ... instrumentation code ...
      except Exception:
log.debug("Could not trace subprocess execution", exc_info=True)
      
return wrapped(*args, **kwargs) # ← Always called, errors propagate
correctly
  ```
 
- **Insufficient error handling tests**: Limited coverage of error
conditions across different subprocess and os functions
- **Parameterized tests** across different configuration scenarios:
  - ASM enabled/disabled combinations
  - IAST enabled/disabled combinations  
  - WAF bypass configurations


## 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
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
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](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

---------

Co-authored-by: Alberto Vara <alberto.vara@datadoghq.com>

Author: github-actions[bot]