fix: Make optional dependencies gracefully optional for tests

[PiGrieco]

🔧 DEPENDENCY FIX: Optional imports for Redis and Schedule

• Made redis import optional in CacheService with graceful fallback
• Made schedule import optional in BackupService with graceful fallback
• Added REDIS_AVAILABLE and SCHEDULE_AVAILABLE flags
• Local cache fallback when Redis not available
• Automatic backup disabled when schedule not available

✅ TEST COMPATIBILITY:

• Resolves ModuleNotFoundError: No module named 'redis'
• Resolves ModuleNotFoundError: No module named 'schedule'
• All 72 tests can now be collected without import errors
• CI/CD unit tests will now pass collection phase

�� REQUIREMENTS UPDATES:

• Added redis>=4.5.0 as commented optional dependency
• Added schedule>=1.2.0 as commented optional dependency
• Clear documentation for optional features

🎯 BENEFITS:

• Core functionality works without optional dependencies
• Enhanced features available when dependencies installed
• Better CI/CD compatibility
• Cleaner development environment setup

The system now gracefully degrades when optional dependencies are not available, ensuring tests can run in minimal environments.