fix(cubefs): round-trip full record envelope through DaemonBackend + gate hardening

- DaemonBackend::put/get now round-trip the FULL record envelope (header+body)
  verbatim via rawput/rawget instead of stripping to a bare body. Before this,
  a socket-backed mount wrote the bare body but get returned it as if it were a
  record, breaking the FUSE read-back path (get_record could not decode it).
  This diverged from the in-memory backend and silently corrupted reads.
- Cargo fmt --check now passes (was failing; the committed tree was never a
  clean ./check, which is why the durable mount could regress undetected).
- Fix two new clippy lints (manual_is_multiple_of) in cubefs/backend.rs and
  cubesys/commands.rs so the -D warnings gate is green.
- Daemon-backed integration tests (cubefs_daemon_smoke, daemon_backend_smoke)
  now use the real CubeStore<DaemonBackend> record path and are #[ignore]d so
  the default gate (no daemon) stays green, while ./check daemon spins up a live
  cube-server and runs them via --ignored. This makes the durable-socket
  contract an actual enforced test, not a manual ad-hoc script.

cubefs/src/bin/cubefs_mount.rs

@@ -49,13 +49,13 @@ fn main() -> ExitCode {
         Some(path) => {
             eprintln!("cubefs: mounting daemon store at socket {path}");
             CubeFs::new(CubeStore::new(
-                Box::new(DaemonBackend::new(path.clone())) as Box<dyn CubeBackend + Send + Sync>,
+                Box::new(DaemonBackend::new(path.clone())) as Box<dyn CubeBackend + Send + Sync>
             ))
         }
         None => {
             eprintln!("cubefs: mounting IN-MEMORY store (writes are NOT durable; use --socket PATH to mount the daemon's store)");
             CubeFs::new(CubeStore::new(
-                Box::new(HashBackend::new()) as Box<dyn CubeBackend + Send + Sync>,
+                Box::new(HashBackend::new()) as Box<dyn CubeBackend + Send + Sync>
             ))
         }
     };