Add crates_io_linecount crate for SLOC analysis

This introduces a new workspace crate that provides line counting functionality using `tokei`. The crate includes `LinecountStats` and `LanguageStats` data structures for storing results, along with core analysis functions for processing file contents.

The implementation includes language filtering to exclude non-programming files and path filtering to skip test and example directories. Comprehensive test coverage is provided with `insta` snapshots to ensure reliable functionality.

This crate provides the foundation for adding SLOC metrics to crates.io by offering a clean, testable interface for analyzing source code statistics.

Author: Turbo87