feat(cast): Implemented cast index (seth feature parity #29)

[psushi]

Motivation

Implemented cast index

Solution

Right now it has the same scope and behaviour as seth index. If there can be a better syntax please do comment.
Note:

• The from_type and to_type is technically not required as cast abi-encode ignores the function signature.
• But cast abi-encode requires that the signature matches the input parameters while seth abi-encode doesn't.
• seth abi-encode "x(address,address)" 42 42 will work but cast abi-encode "x(address,address)" 42 42 won't. Just some observations.

[mattsse]

lgtm!
smol nit

[psushi]

Thanks @mattsse! I have made the changes 👍🏽

[psushi]

@mattsse, one test is failing, is it from my PR?, seems to be from somewhere else, what can I do?

[mattsse]

@mattsse, one test is failing, is it from my PR?, seems to be from somewhere else, what can I do?

unrelated rpc error,

lgtm!