Add support for typing.TypeAliasType #579

import msgspec as ms
from typing import Annotated

NonEmptyStringAlias = Annotated[str, ms.Meta(min_length=1)]
type NonEmptyStringTypeAlias = Annotated[str, ms.Meta(min_length=1)]


class A(ms.Struct):
    name: NonEmptyStringAlias
    
    
class T(ms.Struct):
    name: NonEmptyStringTypeAlias
    
    
print(ms.json.decode(ms.json.encode(A('test')), type=A))

print(ms.json.decode(ms.json.encode(T('test')), type=T))

A(name='test')
...
TypeError: Type 'NonEmptyStringTypeAlias' is not supported

print(type(NonEmptyStringTypeAlias))
# typing.TypeAliasType

print(type(NonEmptyStringAlias))
# typing._AnnotatedAlias

NonEmptyStringTypeAlias.__value__ is NonEmptyStringAlias
# True