chore: Completed test, Fixed advances

[7maylord]

1 Fee Calculation Fixes

• Updated fee calculation logic in tests to properly handle net vs gross amounts
• Fixed rounding issues in fee calculations that were causing 1 wei discrepancies
• Added proper handling of fees in batch disbursement tests

2. Custom Error Handling

• Replaced string error messages with proper custom error selectors
• Added missing imports for CustomErrors library
• Updated revert tests to use correct error selectors:

3. Test Assertions

• Fixed balance assertions to account for fee deductions
• Updated event emission tests to match contract behavior
• Added proper fee collector balance checks

4. Testing

• All tests now pass successfully
• Improved test coverage for edge cases