ci: capture cargo timings in Rust CI and release workflows (#11543)

## Why
We want actionable build-hotspot data from CI so we can tune Rust
workflow performance (for example, target coverage, cache behavior, and
job shape) based on actual compile-time bottlenecks.

`cargo` timing reports are lightweight and provide a direct way to
inspect where compilation time is spent.

## What Changed
- Updated `.github/workflows/rust-release.yml` to run `cargo build` with
`--timings` and upload `target/**/cargo-timings/cargo-timing.html`.
- Updated `.github/workflows/rust-release-windows.yml` to run `cargo
build` with `--timings` and upload
`target/**/cargo-timings/cargo-timing.html`.
- Updated `.github/workflows/rust-ci.yml` to:
  - run `cargo clippy` with `--timings`
  - run `cargo nextest run` with `--timings` (stable-compatible)
- upload `target/**/cargo-timings/cargo-timing.html` artifacts for both
the clippy and nextest jobs

Artifacts are matrix-scoped via artifact names so timings can be
compared per target/profile.

## Verification
- Confirmed the net diff is limited to:
  - `.github/workflows/rust-ci.yml`
  - `.github/workflows/rust-release.yml`
  - `.github/workflows/rust-release-windows.yml`
- Verified timing uploads are added immediately after the corresponding
timed commands in each workflow.
- Confirmed stable Cargo accepts plain `--timings` for the compile phase
(`cargo test --no-run --timings`) and generates
`target/cargo-timings/cargo-timing.html`.
- Ran VS Code diagnostics on modified workflow files; no new diagnostics
were introduced by these changes.

.github/workflows/rust-release.yml

@@ -205,7 +205,14 @@ jobs:
       - name: Cargo build
         shell: bash
         run: |
-          cargo build --target ${{ matrix.target }} --release --bin codex --bin codex-responses-api-proxy
+          cargo build --target ${{ matrix.target }} --release --timings --bin codex --bin codex-responses-api-proxy
+
+      - name: Upload Cargo timings
+        uses: actions/upload-artifact@v6
+        with:
+          name: cargo-timings-rust-release-${{ matrix.target }}
+          path: codex-rs/target/**/cargo-timings/cargo-timing.html
+          if-no-files-found: warn
 
       - if: ${{ contains(matrix.target, 'linux') }}
         name: Cosign Linux artifacts