fix(py-lsp): cap expression evaluation depth

[SyntaxSawdust]

Summary

• Add a Python expression-evaluation depth guard with graceful unknown fallback.
• Track evaluator recursion depth in PyLSPContext.
• Add a fork-protected regression for deeply nested Python expressions.

Why

Fixes #720.

Python was missing the eval-depth protection already present in sibling LSP implementations. Deeply nested Python expressions now stop at a bounded depth instead of continuing recursive type evaluation indefinitely.

Tests

• build/c/test-runner stack_overflow - passed, 14 tests.
• build/c/test-runner py_lsp py_lsp_stress - passed, 102 tests.
• git diff --check - passed.

Scope

• No redesign of Python type inference or call resolution.
• No changes to other language LSP caps.
• Full test/lint were not rerun; local broad proof is environment/tooling-limited as noted above.