test: capture incremental recursive warning loss

[teerthsharma]

Summary

Adds a deterministic regression test for facebook#4216.

A comment-only edit to one member of a recursive two-module binding cycle loses the non-convergent-recursion warning during an incremental recheck, while a fresh check of the byte-identical final sources emits it.

This is a test-only stack on facebook#4188. It targets that PR's head because current main reaches the older capped-propagation failure before this behavior is exposed.

Test shape

• Fixes the worker count at one to remove scheduler variability.
• Asserts the cold result contains non-convergent-recursion.
• Asserts warm and cold diagnostics match.
• Uses #[should_panic] so the regression stays green until the production fix lands.

No production code, dependencies, or documentation are changed.

Verification

• Red phase: the unwrapped test failed with warm [] versus cold ["non-convergent-recursion"].
• Expected-panic phase: cargo test -p pyrefly test_incremental_recursive_warning_survives_comment_edit -- --nocapture
• Formatting/lint: python3 test.py --no-test --no-tensor-shapes --no-conformance --no-jsonschema
• git diff --check