docs: add method docs

[antazoey]

What I did

I have been researching EIP-2678 and thought that this package should be updated. Most of the material is borrowed from the EIP as well as fitting in existing documentation.

How I did it

Read through https://eips.ethereum.org/EIPS/eip-2678#package-name and add bits to PackageManifest and ContractType classes.

How to verify it

Verify the docs make sense that were added

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)