fix(serializer): Don't call __iter__ on arbitrary sequences

[sentrivana]

Description

The serializer will attempt to serialize whatever objects are thrown into it. This includes arbitrary local variables in folks' programs that might have all sorts of side-effects.

Notably, if an object is a Sequence (it has __iter__, __len__, and __getitem__), we will try to __iter__ over it. Which is potentially an unwise thing to do, as we know nothing about the object's custom __iter__ implementation. It can, for example, acquire a non-reentrant lock. In some scenarios, this can lead to deadlocks caused by the SDK.

In this PR, the serializer is changed so that we don't try to __iter__ over all Sequences, just built-in stdlib ones. Of course, nothing is preventing folks from defining side-effecty lists, tuples and sets, but it's a bit less likely to happen than on a custom class. Custom sequences will now be simply __repr__'d.

Issues

• Closes Deadlock during GC with Sentry + Opentelemetry + Tornado + aiohttp #5586
• Closes https://linear.app/getsentry/issue/PY-2124/deadlock-during-gc-with-sentry-opentelemetry-tornado-aiohttp

Reminders

• Please add tests to validate your changes, and lint your code using tox -e linters.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

[linear-code]

PY-2124

[github-actions]

Codecov Results 📊

✅ 282 passed | Total: 282 | Pass Rate: 100% | Execution Time: 43.06s

📊 Comparison with Base Branch

Metric	Change
Total Tests	—
Passed Tests	—
Failed Tests	—
Skipped Tests	—

✨ No test changes detected

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 14891 uncovered lines.
✅ Project coverage is 33.42%. Comparing base (base) to head (head).

Files with missing lines (1)

File	Patch %	Lines
serializer.py	86.10%	⚠️ 26 Missing and 11 partials

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
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+ Coverage    33.42%    33.42%        —%
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  Files          190       190         —
  Lines        22366     22367        +1
  Branches      7594      7594         —
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+ Hits          7475      7476        +1
- Misses       14891     14891         —
- Partials       744       744         —

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[alexander-alderman-webb]

Possibly leads to some data loss but it's worth it to not interfere with users apps IMO.