feat(ci): add mirage/rocjitsu emulation tests

[amd-arosa]

Motivation

rocrtst and most of our other runtime tests need a real GPU to run, which ties
them to our (limited) pool of GPU runners. rocjitsu is a CPU-based GPU emulator —
it executes AMD GPU code objects on the host — and mirage is the CLI that drives
it. Running tests through mirage means we can exercise the runtime on plain CPU
machines, and eventually on architectures we don't have silicon for yet.

This is the first emulation test wired into the matrix. The other goal was to set
it up so adding the next one doesn't require rethinking any of the CI plumbing.

Technical Details

The main idea is that an emulation job picks its runner from the emulator it uses,
not from a hardcoded label. A matrix entry opts in by setting "emulator", and
fetch_test_configurations.py maps that to a node (and whether the node has a
GPU) in _EMULATOR_RUNNERS:

• rocjitsu → rocjitsu-cpu, no GPU
• rocjitsu-dbt → rocjitsu-gpu, has a GPU (dbt offloads to hardware)
• noop → rocjitsu-cpu, no GPU

The script writes the resolved label to emulation_runner, and the GPU container
devices (/dev/kfd, the video groups, etc.) are only added when the node
actually has a GPU. An unknown emulator raises instead of quietly falling through
to a GPU runner. The workflow just reads emulation_runner — same pattern as
multi_gpu_runner — so adding a new backend or node is a one-line change in the
map and no workflow edits.

The rest:

• emulation_utils.py — small helper to find the mirage binary, pick the mirage
  profile for an AMDGPU family, and build the mirage run ... -- <cmd> command.
• test_rocrtst_emulation.py — runs rocrtst64 under rocjitsu. Emulation is
  slow, so it runs the reduced test set by default; set EMULATION_TEST_TYPE=full
  for the whole suite. Families rocjitsu can't emulate are skipped.
• test_mirage_smoke.py — a minimal check that mirage works, using the noop
  backend (no GPU, no rocjitsu runtime needed).

Linux only, since the emulation artifacts are Linux only.

The triggering side lives in a separate rocm-systems PR (emulation changes run the
smoke test; runtimes/all/nightly run rocrtst-emulation), so this PR stands on its
own. Note that the rocjitsu-cpu runner label needs to exist for the jobs to
land somewhere.

Test Plan

mirage and rocjitsu run for real in CI, so locally I checked the matrix output and
the script logic:

• Generated the matrix and confirmed the runner + container options for
  rocrtst-emulation, mirage-smoke, and a rocjitsu-dbt entry.
• Ran test_mirage_smoke.py against a stub mirage.
• Ran test_rocrtst_emulation.py for supported/unsupported families and for
  quick vs full.
• Existing matrix/artifact unit tests, plus a YAML parse of the workflow.

In CI, the plan is to dispatch the multi-arch workflow with
linux_test_labels: test:mirage-smoke (then test:rocrtst-emulation) on a
supported family — gfx942, gfx950, or gfx1250.

Test Result

Everything above passes locally:

• rocjitsu and noop route to rocjitsu-cpu with no GPU devices; rocjitsu-dbt
  routes to rocjitsu-gpu and keeps them; non-emulation jobs are unchanged; a bad
  emulator name raises.
• The mirage smoke script passes end to end.
• rocrtst-emulation picks the mi350x profile for gfx950, uses the reduced filter
  by default, runs the full set with EMULATION_TEST_TYPE=full, shards correctly,
  and skips gfx1151.
• 31 unit tests pass and the workflow YAML parses.

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.

[therock-pr-bot]

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