fix: add missing SecurityConfig properties to Python type stubs

[bug-ops]

Summary

• Adds allowed_extensions: list[str] and banned_path_components: list[str] to SecurityConfig in exarch.pyi
• Both properties have getter/setter implementations in config.rs but were absent from the stubs
• Pyright reported reportAttributeAccessIssue on valid property accesses

Closes #72

Test plan

• Pre-commit checks pass (fmt, clippy, tests)
• Verify pyright no longer reports errors on the reproduction script from [Bug]: Python type stubs are missing two configuration properties #72

[bug-ops]

Verification

Built locally with maturin develop and ran pyright against the reproduction script from the issue:

$ python -m pyright exarch_type_check.py
/tmp/exarch_type_check.py
  /tmp/exarch_type_check.py:4:8 - warning: Import "exarch" could not be resolved from source (reportMissingModuleSource)
0 errors, 1 warning, 0 informations

The reportMissingModuleSource warning is expected for binary extensions (no Python source to resolve from) and is unrelated to the fix. Runtime check also passes.

Before the fix: 8 pyright errors (reportAttributeAccessIssue on every access to banned_path_components and allowed_extensions). After: 0 errors.