build(toolchain): switch Rust channel to stable (#4775)

* Change Rust toolchain channel to stable

Signed-off-by: houseme <housemecn@gmail.com>

* style: apply clippy --fix and cargo fix lint suggestions

Run `cargo clippy --fix --all-targets --all-features` and
`cargo fix --lib --all-targets` across the workspace, then resolve the
remaining warnings by hand:

- collapse needless borrows in `format!` args, prefer `?` over explicit
  early returns, and use `.values()` / `.flatten()` iterator adapters
- rewrite the `Md5` scan loop via `manual_flatten` and re-indent the
  `select!` macro body (rustfmt skips macro interiors)
- annotate the intentional dead-code `Md5` inherent methods (constructed
  only by the test factory) with `#[allow(dead_code)]`

Behavior is unchanged.

Co-Authored-By: heihutu <heihutu@gmail.com>

---------

Signed-off-by: houseme <housemecn@gmail.com>
Co-authored-by: heihutu <heihutu@gmail.com>

crates/ecstore/src/bucket/replication/replication_state.rs

@@ -208,7 +208,7 @@ impl ReplicationStats {
         let now = SystemTime::now();
 
         let cache_read = cache.read().await;
-        for (_bucket, stats) in cache_read.iter() {
+        for stats in cache_read.values() {
             for stat in stats.stats.values() {
                 // Now we can update the moving averages using interior mutability
                 stat.xfer_rate_lrg.measure.update_exponential_moving_average(now);