Parallelize cloud test follow-up jobs

[shchur]

Rebased version of #274 onto current master (that PR has merge conflicts, so GitHub never ran CI on it).

Summary

• keep the general suite limited to generic checks that do not launch SageMaker jobs
• train tabular and timeseries predictors once in a dedicated CI step, then fan out follow-up tests under xdist
• derive the setup and deselection node IDs directly from the module name
• share deterministic job-name, S3-path, and attach-job plumbing through conftest without hiding module-specific prediction behavior
• remove the obsolete multimodal test suite and its disabled workflow job
• pass only the deterministic SageMaker job name between steps; no uploaded manifest or artifact
• cancel superseded CodeQL runs per PR (CI workflow already has this on master)

Testing

• Ruff formatting and static lint pass
• GitHub CI exercises the AWS-backed tests

[github-actions]

Job PR-278-66ff01f is done.
Docs are uploaded to https://d12sc05jpx1wj5.cloudfront.net/PR-278/66ff01f/index.html