ci(cache): Migrate Rust cache to runner-managed multi-level Redis and S3

Centralize cache service management in the Gitea runner for improved persistence and reliability using an SSD-backed S3 backend. This ensures robust verification of multi-tier cache operations.

ci/sccache-stats.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+"""Wait for this job's cache writes/backfills, then print complete statistics."""
+import json
+import subprocess
+import time
+
+end = time.monotonic() + 30
+while True:
+    data = json.loads(subprocess.check_output(
+        ["sccache", "--show-stats", "--stats-format", "json"],
+        timeout=max(0.1, end - time.monotonic()),
+    ))
+    stats = data["stats"]
+    misses = sum(stats["cache_misses"]["counts"].values())
+    levels = stats.get("multi_level") or []
+    writes_done = stats["cache_writes"] + stats["cache_write_errors"] >= misses
+    backfills_done = sum(x["backfills_to"] for x in levels) >= sum(
+        x["backfills_from"] for x in levels
+    )
+    if writes_done and backfills_done:
+        break
+    if time.monotonic() >= end:
+        subprocess.run(["sccache", "--show-stats"], check=True, timeout=5)
+        raise SystemExit("Timed out waiting for sccache writes/backfills")
+    time.sleep(0.1)
+subprocess.run(["sccache", "--show-stats"], check=True, timeout=5)