Support `typing.get_type_hints(partial(fn, ...))` by 'unwrapping' the `partial`, and discarding hints for bound arguments

We added this to Hypothesis' get_type_hints() helper a few years ago, and while most of that function is clearly not suitable to upstream, it struck me recently that "works with functools.partial" could quite reasonably be added to the stdlib function.

It's also plausible that the typing module prefers to avoid calling inspect.signature, though I don't have a great sense of how to determine which parameters have been bound without getting the signature of the partial object. In any case, the implementation need not be the same as in Hypothesis, although as the author you're welcome to use that code if you'd like.

Empieza leyendo la implementación existente de typing.get_type_hints y el helper de Hypothesis referenciado en hypothesis-python/src/hypothesis/internal/compat.py. Comprueba cómo functools.partial e inspect.signature exponen los argumentos enlazados y, después, define pruebas que demuestren que los partials se desenvuelven y que las anotaciones de los argumentos enlazados se descartan. Se considera terminado cuando el comportamiento está cubierto sin romper los casos existentes de get_type_hints.