feat: add retry_unless_exception_cause_type (cycle-safe cause walk)

[MohammedAnasNathani]

Summary

Implements #625 — retry_unless_exception_cause_type, the cause-chain mirror of retry_unless_exception_type / partner to retry_if_exception_cause_type.

Also hardens cause walking with a cycle-safe helper so raise e from e cannot hang the retry loop (#658).

API

@retry(retry=retry_unless_exception_cause_type(NameError), reraise=True)
def call():
    ...

• Keep retrying while no matching type appears in the __cause__ chain
• Stop (do not retry) when a matching cause is found
• Successful outcomes follow the same convention as retry_unless_exception_type

Tests

• Integration: stop immediately when cause is NameError
• Unit: predicate true/false for OSError-vs-NameError causes
• Cycle: self-referential __cause__ terminates

Closes #625
Related: #658

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[MohammedAnasNathani]

Ready for review. Local: 170 tests pass (+ tornado skipped offline); CI green on 3.10–3.14 (check/lint/mypy). Implements #625 with cycle-safe cause walk (#658).

[jd]

This is just noise/churn AFAICT