Make token and stat callback optional in multimodal runner

[pytorchbot]

This PR was created by the merge bot to help merge the original PR into the main branch.
ghstack PR number: #13664 by @jackzhxng
^ Please use this as the source of truth for the PR details, comments, and reviews
ghstack PR base: https://github.com/pytorch/executorch/tree/gh/jackzhxng/32/base
ghstack PR head: https://github.com/pytorch/executorch/tree/gh/jackzhxng/32/head
Merge bot PR base: https://github.com/pytorch/executorch/tree/gh/jackzhxng/31/orig
Merge bot PR head: https://github.com/pytorch/executorch/tree/gh/jackzhxng/32/orig
@diff-train-skip-merge

[pytorch-bot]

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❌ 6 New Failures

As of commit e195233 with merge base 99e6349 ():

NEW FAILURES - The following jobs have failed:

• pull / unittest / linux / linux-job (gh)
  RuntimeError: Command docker exec -t 96a9351433e66afa28ebd017adda4772efde16ed11bf53bb281a3cc240da07e4 /exec failed with exit code 3
• pull / unittest / macos / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 3
• pull / unittest-arm-backend-with-no-fvp (test_pytest_models) / linux-job (gh)
  RuntimeError: Command docker exec -t f4481e3237695fb99207f755fe0d189b96a6a80078e4aec2fed9c2be825dd5ad /exec failed with exit code 3
• pull / unittest-arm-backend-with-no-fvp (test_pytest_ops) / linux-job (gh)
  RuntimeError: Command docker exec -t ca10ed8d2438c63a3d7cb1fe138c6601999c9c2c08de4223d161df92d208dee7 /exec failed with exit code 3
• pull / unittest-editable / linux / linux-job (gh)
  RuntimeError: Command docker exec -t 45a2b8745bef9c27edeca6f822ed6bf6370d4bd624147f158bd7597553557b9d /exec failed with exit code 3
• pull / unittest-editable / macos / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 3

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