refactor: move nightly fmt check to rust_fmt.sh script

Author: CuteChuanChuan

.github/workflows/rust.yml

@@ -587,12 +587,10 @@ jobs:
         uses: ./.github/actions/setup-builder
         with:
           rust-version: stable
-      - name: Setup nightly Rust toolchain
-        run: rustup toolchain install nightly --component rustfmt
       - name: Run cargo fmt check (including doc comments)
         run: |
           echo '' > datafusion/proto/src/generated/datafusion.rs
-          cargo +nightly fmt --all -- --check --config format_code_in_doc_comments=true
+          ci/scripts/rust_fmt.sh
 
   # Coverage job disabled due to
   # https://github.com/apache/datafusion/issues/3678

ci/scripts/rust_fmt.sh

@@ -18,4 +18,10 @@
 # under the License.
 
 set -ex
-cargo fmt --all -- --check
+
+# Install nightly toolchain (skips if already installed)
+rustup toolchain install nightly --component rustfmt
+
+# Use nightly rustfmt to check formatting including doc comments
+# This requires nightly because format_code_in_doc_comments is an unstable feature
+cargo +nightly fmt --all -- --check --config format_code_in_doc_comments=true