rust: hrtimer: Add HrTimerCallbackContext and ::forward()

rust: hrtimer: Add HrTimerCallbackContext and ::forward()

With Linux's hrtimer API, there's a number of methods that can only be
called in two situations:

* When we have exclusive access to the hrtimer and it is not currently
  active
* When we're within the context of an hrtimer callback context

This commit handles the second situation and implements hrtimer_forward()
support in the context of a timer callback. We do this by introducing a
HrTimerCallbackContext type which is provided to users during the
RawHrTimerCallback::run() callback, and then add a forward() function to
the type.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20250821193259.964504-5-lyude@redhat.com
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>