chore(internal): handle additional attributes in module watchdog

[P403n1x87]

Description

PEP 302 documents additional optional methods for the loader. This change adds support for them by proxying attribute requests to the underlying loader instance, when not specifically overridden. The __class__ attribute is also handled specially to allow isinstance to believe that instances of the module watchdog loader are also instances of the underlying actual loader. This is required by some tools, e.g. slotscheck, that can handle only certain known types of loader (e.g. those that come with the Python stdlib).

Checklist

• Title must conform to conventional commit.
• Add additional sections for feat and fix pull requests.
• Ensure tests are passing for affected code.
• Library documentation and/or Datadog's documentation site is updated. Link to doc PR in description.

Reviewer Checklist

• Title is accurate.
• Description motivates each change.
• No unnecessary changes were introduced in this PR.
• PR cannot be broken up into smaller PRs.
• Avoid breaking API changes unless absolutely necessary.
• Tests provided or description of manual testing performed is included in the code or PR.
• Release note has been added for fixes and features, or else changelog/no-changelog label added.
• All relevant GitHub issues are correctly linked.
• Backports are identified and tagged with Mergifyio.
• Add to milestone.

[codecov-commenter]

Codecov Report

Merging #4049 (480efeb) into 1.x (e618c0f) will decrease coverage by 0.76%.
The diff coverage is 49.40%.

❗ Current head 480efeb differs from pull request most recent head 2c02503. Consider uploading reports for the commit 2c02503 to get more accurate results

@@            Coverage Diff             @@
##              1.x    #4049      +/-   ##
==========================================
- Coverage   79.86%   79.10%   -0.77%     
==========================================
  Files         717      718       +1     
  Lines       56347    56717     +370     
==========================================
- Hits        45004    44865     -139     
- Misses      11343    11852     +509     

Impacted Files	Coverage Δ
ddtrace/contrib/flask/patch.py	0.00% <0.00%> (ø)
ddtrace/contrib/pylons/middleware.py	87.05% <ø> (ø)
tests/contrib/django/django_app/settings.py	100.00% <ø> (ø)
tests/contrib/django/test_django.py	100.00% <ø> (ø)
tests/contrib/flask/test_flask_appsec.py	0.00% <0.00%> (ø)
tests/contrib/flask/test_flask_snapshot.py	0.00% <0.00%> (ø)
tests/contrib/flask/test_hooks.py	0.00% <0.00%> (ø)
tests/contrib/flask/test_request.py	0.00% <0.00%> (ø)
tests/contrib/flask/test_static.py	0.00% <0.00%> (ø)
tests/contrib/flask/test_template.py	0.00% <0.00%> (ø)
... and 30 more

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