`Function` type doesn't work with `isinstance` checks

```py
from basedtyping import Function

isinstance(1, Function) # Argument 2 to "isinstance" has incompatible type "object"; expected "type | UnionType | tuple[type | UnionType | tuple[Any, ...], ...]" [arg-type]
```

Start by locating the definition and export of basedtyping.Function, then reproduce the shown isinstance type-checking error with basedmypy. The issue is done when the example accepts Function as the second argument to isinstance without the reported diagnostic.

Written by the indexing model from the issue text.