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

[yafshar]

What?

Add a no-GPU CI lane that builds the UCX Level Zero (ZE) backend and performs a runtime smoke check without requiring Intel GPU hardware.

• Introduce a new ze PR build mode in buildlib/tools/builds.sh
  • Configure with --with-ze
  • Verify HAVE_ZE
  • Build and install UCX
  • Assert that the ZE memory domain (ze_cpy) and transport (ze_copy) enumerate via ucx_info -d
• Runtime hardware detection follows the same availability pattern as build_cuda and build_rocm
  • If an Intel GPU is present: run real hardware smoke tests
  • Otherwise: fall back to the Level Zero null driver (synthetic device)
  • Optional require_real_ze disables fallback for validation on GPU nodes
• Add a new builder image buildlib/dockers/ze-builder.Dockerfile
  • Based on intel/oneapi-toolkit:2026.0.0-devel-ubuntu24.04
  • Uses the shipped ZE loader and headers
  • Builds the in-tree Level Zero null driver from a tag matching the loader version (v1.27.0)
  • Installs only the versioned libze_null.so.*
• Add a new ubuntu2404_ze container resource and x86_64 CI matrix lane
• Update az_init_modules to return early when Environment Modules are not present

Why?

UCX includes a ZE backend (src/uct/ze) but currently lacks CI coverage, allowing regressions to land undetected.

This change:

• Adds a --with-ze CI build
• Provides a basic runtime validation path
• Enables testing without requiring physical hardware

Real Intel GPU nodes are not available in upstream CI, so the lane uses the
Level Zero loader's null driver (ZE_ENABLE_NULL_DRIVER=1) to provide a
synthetic device for a hardware-independent smoke path.

The null driver is not shipped by the Level Zero release/runtime packages, so
the builder image builds it from Level Zero source at the tag matching the
loader version. Setting ZE_ENABLE_NULL_DRIVER=1 only enables the loader path;
without libze_null.so.* installed, the loader finds no null-driver library and
reports zero devices — which is why the image installs the built driver.

How?

• The null driver so name is versioned (libze_null.so.<loader_version>)
• The Dockerfile detects the loader version and builds the matching Level Zero tag
• Only libze_null.so.* is installed, leaving the system loader intact

build_ze() runtime behavior:

• Runs ucx_info -d without null driver variables
• If ze_copy enumerates: use real hardware
• Otherwise: fall back to the null driver

This ensures:

• Consistent behavior across environments
• Automatic use of hardware when available
• Fully hardware-independent CI

Verification

Validated on a no-GPU x86_64 host:

• Image build detects loader 1.27.0 and installs libze_null.so.1.27.0
• zello_world runs successfully under the null driver
• UCX builds with --with-ze and reports HAVE_ZE=1
• Real-device probe returns zero devices and triggers fallback
• ucx_info -d enumerates ze_cpy and ze_copy

CI Image

The builder image is published and referenced directly in main.yml:

• intel/ucx-ze-builder:oneapi-2026.0.0-l0-1.27.0

The ubuntu2404_ze lane pulls this image directly. A companion source image,
intel/ucx-ze-builder-sources, provides the corresponding source for the open
source components distributed in the builder image.

[yafshar]

@yosefe @brminich @tvegas1, this PR adds the ZE CI coverage requested in #11218: a ze build mode in builds.sh that configures UCX with --with-ze, verifies HAVE_ZE, and checks that ze_cpy and ze_copy are enumerated by ucx_info.

Regarding the mock-library question, the Level Zero loader's null driver exposes a synthetic device, allowing the lane to run on GPU-less CI workers. The null driver is not included in the Level Zero release packages, so buildlib/dockers/ze-builder.Dockerfile builds it from the source tag matching the loader. The resulting image is published as intel/ucx-ze-builder on Docker Hub and used directly by the ubuntu2404_ze lane.

The build mode can also use a real Intel GPU when the container is given access to one; otherwise it falls back to the null driver. Ready for review.

[yafshar]

Thanks for the review @Alexey-Rivkin. CI is fully green (162/162, including the
new ubuntu2404_ze lane) and there are no outstanding comments.

@dpressle when you get a chance, could you take a look? This is CI/build-only
(buildlib/), no changes under src/. Happy to rebase or update if that helps review.