- Replace nested if-let statements with let-chain pattern for VmRSS memory parsing in /proc/self/status
- Replace nested if-let statements with let-chain pattern for Redis used_memory parsing
- Wrap std::env::set_var calls in unsafe blocks in validation_tests.rs for MAX_BYTES_LIMIT and MAX_AMOUNT_LIMIT
- Add credit_management_tests.rs with tests for SubscriberAccount, UsageEvent, UsageType, AccountStatus, and integer arithmetic operations
- Add error_tests.rs with tests for ChargingError Display implementation, cloning, and log_error function
- Add rating_billing_tests.rs with tests for ChargingRule variants, as_str conversion, billing period parsing, timestamp filtering, and cost calculations
- Add validation_tests.rs with tests for validate_bytes, validate