[Test] Consolidate test cleanup and CI taxonomy (net -11.4K lines) (#37436)

Co-authored-by: Mick Qian <mickqian@users.noreply.github.com>

test/registered/e2e/diffusion/test_diffusion_bcg.py

@@ -0,0 +1,13 @@
+from sglang.test.ci.ci_register import register_cuda_ci
+from sglang.test.ci.diffusion_suite_bridge import run_diffusion_suite
+
+# ci-cost-override: compatibility bridge preserves the existing diffusion lane.
+register_cuda_ci(
+    est_time=3600,
+    stage="base-b",
+    runner_config="diffusion-bcg-1-gpu-h100",
+)
+
+
+if __name__ == "__main__":
+    run_diffusion_suite("bcg-diffusion")