Use rustfmt directly in prek (#22508)

## Summary

Apparently this is about ~18x faster (2.25s → 0.12s) for a single-file
change, and ~2x faster (2.36s → 1.25s) for `prek run -a`.

.github/workflows/ci.yaml

@@ -778,9 +778,6 @@ jobs:
         with:
           persist-credentials: false
       - uses: astral-sh/setup-uv@61cb8a9741eeb8a550a1b8544337180c0fc8476b # v7.2.0
-      - uses: Swatinem/rust-cache@779680da715d629ac1d338a641029a2f4372abb5 # v2.8.2
-        with:
-          save-if: ${{ github.ref == 'refs/heads/main' }}
       - uses: actions/setup-node@395ad3262231945c25e8478fd5baf05154b1d79f # v6.1.0
         with:
           node-version: 24
@@ -794,7 +791,7 @@ jobs:
           echo '```console' > "$GITHUB_STEP_SUMMARY"
           # Enable color output for prek and remove it for the summary
           # Use --hook-stage=manual to enable slower hooks that are skipped by default
-          SKIP=cargo-fmt uvx prek run --all-files --show-diff-on-failure --color always --hook-stage manual | \
+          SKIP=rustfmt uvx prek run --all-files --show-diff-on-failure --color always --hook-stage manual | \
             tee >(sed -E 's/\x1B\[([0-9]{1,2}(;[0-9]{1,2})*)?[mGK]//g' >> "$GITHUB_STEP_SUMMARY") >&1
           exit_code="${PIPESTATUS[0]}"
           echo '```' >> "$GITHUB_STEP_SUMMARY"