improve Data typing

[trim21]

Data does not need to be a Mapping[str, Any] but just object with keys and __getitem__

This make it possible to use some dict-like object, for example asyncpg.Record without typing error.

for example, asyncpg.Record has keys() -> Iterable[str] bot not keys() -> KeysView[str], and we convert keys to set so it also doesn't need keys to return KeysView

before:

row = pg.fetchrow(...)
v = from_dict(..., row) # mypy raise typing error, asyncpg.Record doesn't satisfy Mapping[str, Any]

[trim21]

@konradhalas hi, is it possible to get a code review on this PR?

[trim21]

@mciszczon can you take a look?

[mciszczon]

@mciszczon can you take a look?

Thanks for pinging me @trim21, seems like a fairly unproblematic addition. Let me ensure it doesn't break anything and we can probably merge it in upcoming days, and sketch out a new release together with #269.