Adds a new decay parameter for a total of 21 parameters.

FSRS 6.0 Integration

Changes

• Updated FSRS dependency to version 6.0
• Added support for FSRS 6.0 parameters with 21 weights (including decay parameter)
• Added decay field to card data structure
• Updated forgetting curve calculation to use decay parameter
• Modified deck configuration to support FSRS 6.0 parameters
• Updated simulator and retention calculation logic for FSRS 6.0

Key Features

1. Decay Parameter Support
   • Added decay field to card data structure
   • Default decay values:
     • FSRS 6.0: 0.2
     • FSRS 4.5/5.0: 0.5
   • Updated forgetting curve calculation to use decay parameter
2. Parameter Management
   • Added fsrs_params_6 field to deck configuration
   • Maintained backward compatibility with FSRS 4.5 and 5.0 parameters
   • Updated parameter optimization and simulation logic
3. UI Updates
   • Modified forgetting curve visualization to account for decay
   • Updated deck options interface to support FSRS 6.0 parameters

Technical Details

• Updated protobuf definitions to include decay field
• Modified memory state handling to include decay parameter
• Updated SQLite storage to handle new decay field
• Adjusted simulator configuration for FSRS 6.0 parameters

Dependencies

• Updated FSRS dependency to latest version
• Updated various Rust dependencies to compatible versions

Testing

• Updated test cases to handle new decay parameter
• Modified forgetting curve tests to account for decay
• Updated simulator tests for FSRS 6.0 parameters

Notes

• This update maintains backward compatibility with existing FSRS 4.5 and 5.0 configurations
• Users can continue using their existing parameters until they choose to upgrade to FSRS 6.0
• The decay parameter provides more flexibility in forgetting curve modeling