BUILD/CI: Add ZE null-driver build and smoke check (#11569)

* BUILD/CI: Add ZE null-driver build and smoke check

Add a "ze" PR build mode that configures UCX with --with-ze, verifies
HAVE_ZE is detected, and checks that the ZE memory domain (ze_cpy) and
transport (ze_copy) are enumerated via ucx_info.

Run this build in a new ubuntu2404_ze container derived from the Intel
oneAPI toolkit image. The container provides the Level Zero loader and
headers, and includes the in-tree Level Zero null driver. When no real
Intel GPU is present, the null driver exposes a synthetic device,
allowing ZE build and basic runtime coverage on GPU-less CI workers.

Provide an opt-in require_real_ze path that disables the null fallback
and fails unless a real GPU is detected, for validation on Intel GPU
nodes.

Update az_init_modules to return early when the Environment Modules
system is unavailable, since the public Intel container does not include
it.

Signed-off-by: Yaser Afshar <yaser.afshar@intel.com>

* BUILD/CI: Use mirrored ZE builder image from internal registry

Pulling the ZE builder from Docker Hub is subject to anonymous pull
rate limits, which intermittently fail CI. Point the ubuntu2404_ze
container at the internal mirror, matching every other container in
the pipeline, and update the Dockerfile publish note accordingly.