tests/timer_api: Fix absolute timeout logic

The test_timeout_abs case had baked in similar mistakes to the
off-by-one in the absolute timer implementation.  FOR THE RECORD:

If you have an absolute timeout expiration set for a tick value "N",
and the current time returned by k_uptime_ticks() is "T", then the
time returned (at the same moment) by any of the *_remaining_ticks()
APIs must ALWAYS AND FOREVER BE EXACTLY "N - T" (also: "N - T > 0"
always, until the moment the kernel ISR hands off control to the first
timeout handler expiring at that tick).

The tick math is exact.  No slop is needed on any systems, no matter
whether their clocks divide by milliseconds or not.

The only gotcha is that we need to be sure that the calls don't
interleave with a real time tick advance, which we do here with a
simple retry loop.

But, about slop... This patch also includes a related fix for the
test_sleep_abs().  On an intel_adsp (which has 50 kHz ticks, a
comparatively slow idle resume and interrupt entry, and even has two
CPUs to mess with latency measurements) I would occasionally see the
k_sleep() take more than a tick to wake up from the interrupt handler
until the return to application code.  Add some real time slop there
(just 100us) to handle systems like this.

Fixes #32572

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>