Font management and text shaping for par-term terminal emulator.

This crate provides:

• Font loading with system font discovery and fallback chains
• Unicode range-specific font mappings (e.g., CJK, emoji)
• HarfBuzz-based text shaping via rustybuzz for ligatures and complex scripts
• Grapheme cluster detection for proper Unicode rendering

Architecture

The FontManager orchestrates font loading and glyph lookup across a priority-ordered chain of fonts:

1. Primary font (with bold/italic/bold-italic variants)
2. Unicode range-specific fonts
3. System fallback fonts

The TextShaper provides HarfBuzz-based text shaping with LRU caching for performance.