ci: run Python checks on ARC runners

[sipercai]

Description

Move the generated Python Test/Lint CI workflows onto the loongsuite-python-arc
ARC runner scale set and reduce job fan-out by batching tox environments with
tox run-parallel -p 4.

This PR intentionally keeps ACK/ACS runner deployment details out of the public
repository. The runner image, ImageCache, Helm values, registry location, and
cluster rebuild runbook are maintained on the cluster/internal documentation
side. The public repository only needs the GitHub Actions runner label used by
the generated workflows.

Generated Misc and LoongSuite Misc jobs stay on GitHub-hosted
ubuntu-latest because they include Docker, precommit, docs, and generation
checks that should not depend on the ACS Python runner pods.

Prior fork validation of the same ARC batching approach reduced the broad CI
wall time from about 48 minutes to about 19 minutes.

Type of change

• Bug fix
• New feature
• Breaking change
• This change requires a documentation update
• CI infrastructure change

How Has This Been Tested?

• tox -e generate-workflows
• python -m py_compile .github/workflows/generate_workflows.py .github/workflows/generate_workflows_loongsuite.py .github/workflows/generate_workflows_lib/src/generate_workflows_lib/__init__.py
• Parsed all .github/workflows/*.yml with PyYAML
• python "$PIPELINE_SKILL_DIR/scripts/check_loongsuite_pr_readiness.py" --repo .
• PRE_COMMIT_HOME="$(mktemp -d)" tox -e precommit
• git diff --check && git diff origin/main...HEAD --check
• Privacy scan over the branch diff found no credentials, private paths, registry image references, or ImageCache IDs

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

Changelog, unit-test, and documentation additions are N/A because this is a
generated CI workflow change. It does not change package runtime behavior.

Validation Evidence

• Spec/scope: CI infrastructure migration based on validated ACK/ACS ARC runner setup.
• Changed surface: workflow generator/templates and generated workflow files.
• Excluded surface: ACK/ACS Helm values, runner image build files, registry image tags, ImageCache manifests, and cluster runbooks.
• Static readiness: pass; only warning is no changed instrumentation plugin, expected for CI infra.
• Precommit: pass with a fresh PRE_COMMIT_HOME.
• Workflow generation: pass; generated workflow files committed.
• YAML parse: pass for 22 workflow files.
• Privacy scan: pass; no credentials, private paths, registry image references, or ImageCache IDs in the branch diff.
• CI: pending after branch update.

Runtime and Telemetry Matrix

Runtime scenarios, GenAI telemetry checks, and Weaver live-check are N/A because
this PR only changes generated CI workflows. It does not change runtime package
behavior, instrumentation behavior, span attributes, or telemetry export paths.

[123liuziming]

LGTM