ci: add current-only validation runner

[weloMThreads]

Add a manual current-only validation script based on pr-validation.yml.

Changes:

• Add run_current_only_validation.sh at repo root.
• Start from installing an already-built tensorflow_musa wheel.
• Do not fetch, checkout, clean, build, or run baseline.
• Run all current-only validation jobs by default:
  integration, fusion, t_accuracy, t_perf, bd_model1, bd_model2, bd_model3,
  onetrans_perf, tokenlarge_perf, training.
• Keep CURRENT_ONLY_JOBS override for partial manual runs.
• Write logs under current_only_logs/current/<RUN_ID>/.

Validation:

• bash -n run_current_only_validation.sh
• ./run_current_only_validation.sh --help