These functions should be safe to use without the Python GIL as they are
not creating or destroying Python objects. So mark them as such.

Note: This does **not** actually release the GIL. We still have to do
that ourselves. However this allows us to use these in code sections
where we have already released the GIL. We can also continue to use them
when we have the GIL as well.

Cython already infers these are `object` type given the assignment type.
So these definitions can be dropped without any loss in affect. This
will make it easier to move the assignment into the GIL block later.

As these functions are effectively called from `nogil` contexts now
given the C functions calling them are `nogil`, make them `nogil` as
well, but acquire the GIL internally for the parts of the function that
require it. Namely when the Python callback is run and its results are
added to the asyncio Future.

Go ahead and release the GIL before calling UCX functions. They should
not be creating, destroying, or modifying any Python objects. Once any
of our callbacks are called that do need to manipulate Python objects,
we make sure to reacquire the GIL anyways.

As this is the type expected by the C level functions that we call later
when using `port`, go ahead and coerce it to `uint16_t` in advance.
This should make it easier to release the GIL later on.