refactor: implement native periodic thread

[P403n1x87]

This PR re-implements the periodic service to use a periodic thread implemented in C++. The reason for doing this is to reduce the dependency of the library on the threading module, which is the source of issues when it comes to frameworks such as gevent.

This is the first step towards a refactoring that is aimed at removing the dependency on the threading module entirely, potentially leading to phasing out the module cloning mechanism, which is what we currently have in place to support frameworks such as the already mentioned gevent.

Testing strategy

The existing test suite provides already many reliable test cases that can give us good confidence about the proposed changes. Further testing is being performed in internal environments.

Performance

We do not expect any particular performance impact from this change

Checklist

• Change(s) are motivated and described in the PR description.
• Testing strategy is described if automated tests are not included in the PR.
• Risk is outlined (performance impact, potential for breakage, maintainability, etc).
• Change is maintainable (easy to change, telemetry, documentation).
• Library release note guidelines are followed. If no release note is required, add label changelog/no-changelog.
• Documentation is included (in-code, generated user docs, public corp docs).
• Backport labels are set (if applicable)

Reviewer Checklist

• Title is accurate.
• No unnecessary changes are introduced.
• Description motivates each change.
• Avoids breaking API changes unless absolutely necessary.
• Testing strategy adequately addresses listed risk(s).
• Change is maintainable (easy to change, telemetry, documentation).
• Release note makes sense to a user of the library.
• Reviewer has explicitly 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
• If this PR touches code that signs or publishes builds or packages, or handles credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

[brettlangdon]

Running flask-simple locally:

Benchmark	ddtrace==2.8.3	native periodic thread
flasksimple-profiler	701 us	686 us: 1.02x faster
flasksimple-debugger	595 us	557 us: 1.07x faster
flasksimple-iast-get	560 us	550 us: 1.02x faster
flasksimple-appsec-get	1.21 ms	1.13 ms: 1.07x faster
flasksimple-appsec-post	1.01 ms	1.03 ms: 1.02x slower
Geometric mean	(ref)	1.02x faster

Benchmark hidden because not significant (3): flasksimple-baseline, flasksimple-tracer, flasksimple-appsec-telemetry

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 2.85714% with 34 lines in your changes are missing coverage. Please review.

Project coverage is 10.19%. Comparing base (33b1a94) to head (b2a1664).

Files	Patch %	Lines
ddtrace/internal/periodic.py	7.14%	13 Missing ⚠️
tests/internal/test_forksafe.py	0.00%	10 Missing ⚠️
tests/appsec/appsec/test_remoteconfiguration.py	0.00%	4 Missing ⚠️
tests/internal/test_periodic.py	0.00%	3 Missing ⚠️
tests/conftest.py	0.00%	2 Missing ⚠️
tests/subprocesstest.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #7659       +/-   ##
===========================================
- Coverage   76.15%   10.19%   -65.96%     
===========================================
  Files        1287     1257       -30     
  Lines      121888   120004     -1884     
===========================================
- Hits        92818    12235    -80583     
- Misses      29070   107769    +78699     

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[emmettbutler]

@P403n1x87 this seems to be a proximate cause of failures like this on main.