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/lifecycle/bucket_lifecycle_ops.rs

@@ -2312,7 +2312,7 @@ pub fn gen_transition_objname(bucket: &str) -> Result<String, Error> {
     let mut hasher = Sha256::new();
     hasher.update(format!("{}/{}", runtime_sources::deployment_id().unwrap_or_default(), bucket).as_bytes());
     let hash = rustfs_utils::crypto::hex(hasher.finalize().as_slice());
-    let obj = format!("{}/{}/{}/{}", &hash[0..16], &us[0..2], &us[2..4], &us);
+    let obj = format!("{}/{}/{}/{}", &hash[0..16], &us[0..2], &us[2..4], us);
     Ok(obj)
 }