Keys and values could be narrower for closed TypedDicts

I was very excited to try out mypy 2.2 with the initial support for the TypedDict closed keyword.
But in our code base, where we often iterate over TypedDicts, it did not help much because the keys and values are still inferred as str and object, respectively.

from typing_extensions import TypedDict, reveal_type


class Closed(TypedDict, closed=True, total=False):
    a: int
    b: str

c = Closed(a=1, b='a')
reveal_type(c.items())

for key, val in c.items():
    c[key]

$ mypy --pretty test.py
test.py:9: note: Revealed type is "_collections_abc.dict_items[str, object]"
test.py:12: error: TypedDict key must be a string literal; expected one of ("a", "b")  [literal-required]
        c[key]
          ^~~
Found 1 error in 1 file (checked 1 source file)

ty narrows both keys and values here

$ ty check test.py
ty check test.py 
info[revealed-type]: Revealed type
 --> test.py:9:13
  |
9 | reveal_type(c.items())
  |             ^^^^^^^^^^ `dict_items[Literal["a", "b"], int | str]`
  |

Found 1 diagnostic

Comienza reproduciendo el ejemplo test.py del issue con mypy --pretty, centrándote en TypedDict.items() y en el acceso posterior c[key]. Traza la ruta de comprobación de tipos de TypedDict responsable de estos tipos inferidos; se considera terminado cuando la iteración sobre un TypedDict cerrado revela una unión literal de claves y los tipos de valor correspondientes, y se acepta el acceso mediante índice con la clave iterada.