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/rio/src/compress_reader.rs

@@ -153,7 +153,7 @@ where
             }
             *this.buffer = out;
             *this.pos = 0;
-            this.temp_buffer.truncate(0); // More efficient way to clear
+            this.temp_buffer.clear(); // More efficient way to clear
             let to_copy = min(buf.remaining(), this.buffer.len());
             buf.put_slice(&this.buffer[..to_copy]);
             *this.pos += to_copy;