Emit json schema defaults for dataclass and attrs default_factory fields - #1222

msgspec.json.schema sets "default" for a Struct field with a list/dict/set/bytearray default_factory (#1183), but not for the same field on a dataclass or attrs class:

@dataclasses.dataclass
class D:
    x: list[int] = dataclasses.field(default_factory=list)

msgspec.json.schema(D)["$defs"]["D"]["properties"]["x"]
# {'type': 'array', 'items': {'type': 'integer'}}

This applies the Struct rule to the dataclass/attrs/TypedDict branch. test_dataclass_or_attrs now expects "default": {} for its dict factory field.