feat(core): implement LogWatcher with Observer Pattern
- Create LogWatcher using Observer Pattern for loose coupling
- Implement compiled regex patterns for EU chat.log parsing:
- Global/HoF detection
- Regular loot parsing
- Skill gain tracking
- Weapon decay monitoring
- Add async polling loop (1s interval for 60+ FPS compliance)
- Implement MockLogGenerator for testing
- Efficient file seeking (only reads new lines)
- Event types: global, hof, loot, skill, decay, kill, enhancer_break
Performance optimized: minimal CPU, non-blocking async.
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