v2.0.0b30

fix: respect umask when creating filelock lock files

The filelock library uses os.chmod() which ignores umask, causing lock
files to be created with 0o644 permissions regardless of umask settings.
This prevented group-writable permissions when umask 002 was set.

Added centralized wrapper functions (create_file_lock and
create_async_file_lock) that calculate the effective mode by applying
the current umask to a base mode of 0o666. This ensures lock files
respect umask settings, allowing group write permissions when umask
allows it (e.g., umask 002 results in 0o664).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>