Make default validation cheap, make full validation optional

[sneakers-the-rat]

When just opening a file, usually we don't care too much about all the validity checks, that's mostly for us when we're checking if something's wrong. the validations end up taking a long freaking time for very large torrents because there are several big iterations in there, so we should

• change the general behavior of instantiating the Torrent model to exclude all but the necessary validations
• make a decorator for the validators that allows us to declare some validation types/scopes/profiles and etc, like

@field_validator("whatever", mode="after")
@validation_scope("pieces", "something-else")
def some_validation_function(...): ...

So that we can then use the context like

Torrent.model_validate(data, context={"tm_validation": ["pieces"]})
# or
Torrent.model_validate(data, context={"tm_validation": ["all"]})

• make a torrent_validate method that is a shortcut to that
• accept validation modes in read()