TypeError from inspect.type_info with unhashable Annotated metadata

[peterschutt]

Description

MCVE

from typing import Annotated

import msgspec


class Test(msgspec.Struct):
    a: Annotated[int, {"unhashable": "metadata"}]


t = Test(a=1)

print(t.a)  # 1 (no runtime issues)

msgspec.inspect.type_info(Test)  # TypeError: unhashable type: 'dict'
 

Error

 Traceback (most recent call last):
  File "/home/peter/PycharmProjects/msgspec-mcve/main.py", line 14, in <module>
    msgspec.inspect.type_info(Test)
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 614, in type_info
    return multi_type_info([type])[0]
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 580, in multi_type_info
    return _Translator(types).run()
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 721, in run
    return tuple(self.translate(t) for t in self.types)
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 721, in <genexpr>
    return tuple(self.translate(t) for t in self.types)
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 755, in translate
    out = self._translate_inner(t, args, **constrs)
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 903, in _translate_inner
    type=self.translate(hints[name]),
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 724, in translate
    t, args, metadata = _origin_args_metadata(typ)
  File "/home/peter/PycharmProjects/msgspec-mcve/venv/lib/python3.10/site-packages/msgspec/inspect.py", line 622, in _origin_args_metadata
    origin = _CONCRETE_TYPES.get(t)
  File "/usr/lib/python3.10/typing.py", line 1651, in __hash__
    return hash((self.__origin__, self.__metadata__))
TypeError: unhashable type: 'dict'

There doesn't seem to be any hard requirement that type metadata via Annotated must be hashable (searching for "hash" in pep 593 doesn't yield anything), however, the implementation of _AnnotatedAlias.__hash__() does hash any metadata as well as the origin type (ref):

    def __hash__(self):
        return hash((self.__origin__, self.__metadata__))