Panic on poisoned parser mutexes in tree-sitter parsing

[jssblck]

Summary

• Make tree-sitter parser lock failures explicit instead of silently turning poisoned mutexes into missing parses.
• Keep syntax matching behavior honest: poisoned parser state now surfaces as a programmer error instead of returning None and hiding the failure.
• Add a regression test that poisons a mutex and verifies the parser helper panics as intended.

Testing

• cargo fmt --all --check
• cargo test -p nudge
• git diff --check

Resolves #13