feat: disallow mutation of abi type

[banteg]

What I did

Disallowed mutation of ABIType, there is no reason to modify it after instantiation.

How I did it

How to verify it

Checklist

• [ ] Passes all linting checks (pre-commit and CI jobs)
• [ ] New test cases have been added and are passing
• [ ] Documentation has been updated
• [ ] PR title follows Conventional Commit standard (will be automatically included in the changelog)