rust: auxiliary: generalize Registration over ForLt

rust: auxiliary: generalize Registration over ForLt

Generalize Registration<T> to Registration<F: ForLt> and
Device::registration_data<F: ForLt>() to return Pin<&F::Of<'_>>.

The stored 'static lifetime is shortened to the borrow lifetime of &self
via ForLt::cast_ref; ForLt's covariance guarantee makes this sound.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Eliot Courtney <ecourtney@nvidia.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260525202921.124698-24-dakr@kernel.org
[ Use PhantomData<F::Of<'a>> instead of
  PhantomData<(fn(&'a ()) -> &'a (), F)>], which also gets us rid of
  #[allow(clippy::type_complexity)]. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>