feat: eth_call state override for contract methods

[banteg]

• fix: inconsistency between __call__ and call arguments in OverloadedMethod
• feat: add state override support to contract calls
• docs: add docs about eth_call override

What I did

Added basic support for state override feature of eth_call. It allows ephemerally changing the state of any addresses before call, including balance, nonce, code, storage slots.

How I did it

Added an optional override argument to ContractCall and to everything that plugs into it.

How to verify it

See example provided in the docs.

Checklist

• I have confirmed that my PR passes all linting checks
• I have included test cases
• I have updated the documentation
• I have added an entry to the changelog