fix(iast): backport fix from 10706 to 2.12 (#10736)

## Description

Partial backport of the Initializer atexit fix from #10706.

## 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)

---------

Signed-off-by: Juanjo Alvarez <[email protected]>

ddtrace/appsec/_iast/_taint_tracking/_native.cpp

@@ -72,6 +72,12 @@ PYBIND11_MODULE(_native, m)
     }
 
     initializer = make_unique<Initializer>();
+    // Create an atexit callback to clean up the Initializer before the interpreter finishes
+    auto atexit_register = py::module_::import("atexit").attr("register");
+    atexit_register(py::cpp_function([]() {
+        initializer->reset_context();
+        initializer.reset();
+    }));
     initializer->create_context();
 
     m.doc() = "Native Python module";

releasenotes/notes/initializer-atexit-6f9a025488fe14b4.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Code Security: ensure the ``Initializer`` object is always reset and freed before the Python runtime.