feat: enhance splikit with multi-threading, memory management, and do…

[Arshammik]

…cumentation (closes #16)

Major enhancements and fixes:

Performance Improvements:

• Add multi-threading support for find_variable_genes with sum_deviance method
• Implement intelligent memory management in make_m2() with batched processing
• Add parallel processing capabilities for large-scale junction data

Function Enhancements:

• make_junction_ab: Add verbose logging and multi-mapped junction filtering options
• make_m1: Add min_counts filtering and verbose parameters
• make_m2: Add batch_size, memory_threshold, force_fast, and multi_thread parameters
• find_variable_genes: Add n_threads parameter for parallel processing
• get_pseudo_correlation: Add metric selection (Cox-Snell/Nagelkerke) and sparse matrix support

Documentation Updates:

• Fix non-ASCII characters in verbose output (replaced with ASCII alternatives)
• Update all Roxygen2 documentation for modified functions
• Sync docs/README.md with all recent parameter changes
• Add comprehensive examples and parameter descriptions

Infrastructure:

• Add pkgdown configuration with minimal theme
• Add GitHub Actions workflow for automatic site building
• Update version to 1.0.5
• Update .Rbuildignore to exclude pkgdown files

This release significantly improves performance for large datasets while maintaining backward compatibility and adding comprehensive documentation.

Fixes #16