Release v0.9.4

Release v0.9.4 (2025-07-10)

Modularized export logic into export_utils.py (pdf/txt/json)
Modularized filetype extraction into filetype_utils.py
Added caching system with calculate_query_hash() for search results
Separated hashing logic into calculate_hash(content) and calculate_query_hash(term, args)
Integrated .msg and .eml file support with metadata-based virtual tags
Moved virtual tag extraction logic into extract_virtual_tags() in fts_core.py
Improved import structure to avoid circular dependencies