Fix HttpAuthenticationType to add callable

[MtkN1]

Add a callable object to the HttpAuthenticationType type definition.

A type checking error occurs when a callable object is given as the auth argument.

Reproduction code

```python import niquests def pizza_auth(request: niquests.PreparedRequest) -> niquests.PreparedRequest: if request.headers: request.headers["X-Pizza"] = "Token" return request def test_callable_auth(): r = niquests.get("https://httpbin.org/get", auth=pizza_auth) print(r.json()["headers"]) if __name__ == "__main__": test_callable_auth() ```

This is allowed at runtime.

https://github.com/jawah/niquests/blob/d83ab6b98e317bbf82ea950a693fce1fc95936a3/src/niquests/models.py#L615-L647