add module level benchmark for gemma3 model

[Gasoonjia]

Stack from ghstack (oldest at bottom):

• gemma3 e2e runner on cuda #15282
• -> add module level benchmark for gemma3 model #15241
• make aoti_torch_empty_strided support creating incontiguous tensor #15228

This diff adds a module-level benchmark for the GEMMA3 model.
Also introduce mutlmodal_benchmark.cpp to replace original voxtral_runner.cpp for benchmarking both gemma3 and voxtral model in module level.

Differential Revision: D84958564

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/15241

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❌ 3 New Failures, 1 Cancelled Job, 1 Unrelated Failure

As of commit acb7e83 with merge base 7349bb5 ():

NEW FAILURES - The following jobs have failed:

• pull / unittest / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_mv3_model
• pull / unittest-editable / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_mv3_model
• pull / unittest-nxp-neutron / linux-job (gh)
  RuntimeError: Command docker exec -t 6caa94c2c1b4b86f322843567cad815d6a8c8709122d3b456c64ba0578cbb464 /exec failed with exit code 1

CANCELLED JOB - The following job was cancelled. Please retry:

• pull / unittest-editable / linux / linux-job (gh)
  ##[error]The operation was canceled.

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• pull / unittest / linux / linux-job (gh) (matched linux rule in flaky-rules.json)
  The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.

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