Adds kwargs passthrough for dataclass construction that was missing

[bnorick]

I added kwarg passthrough for any time datafiles creates a dataclass for you. The following example illustrates:

# in main
@datafiles.datafile('{self.a}.toml', manual=True)
@dataclasses.dataclass(frozen=True)
class T:
    a: int
    b: int = 2

# becomes
@datafiles.datafile('{self.a}.toml', manual=True, frozen=True)
class T3:
    a: int
    b: int = 2