Pin the Rust toolchain to 1.95.0 (#57373)

## What changed

- Replace Rust `1.99.1` pins with `1.95.0` across Cargo, Bazel, CI, release workflows, and Windows setup, and update the Bazel lockfile.
- Adjust Rust APIs, borrowing, and lint-related code for the pinned toolchain, and box MCP tool dispatch to bound compiler async-layout query depth.
- Update the halfwidth sound mark snapshot and allow optional symbol hash suffixes in the code mode host package smoke test.

GitOrigin-RevId: 75460c3d0465dc601811e619bce373a4f7ff2912

codex-rs/exec/src/lib.rs

@@ -2321,9 +2321,7 @@ fn decode_utf16(
     }
 
     let units: Vec<u16> = input
-        .as_chunks::<2>()
-        .0
-        .iter()
+        .chunks_exact(2)
         .map(|chunk| decode_unit([chunk[0], chunk[1]]))
         .collect();