Remove dirs dependency to fix Cargo.lock duplicates

- Replace dirs::cache_dir() with manual XDG_CACHE_HOME logic
- Fixes duplicate windows_x86_64_msvc entries (had 3, now 2)
- Uses std::env vars for cross-platform cache directory
- Run cargo update to update all dependencies to latest MSRV
- All 61 tests still passing
- Cache functionality verified working

Author: quantum-encoding