Retry extension Cargo dependency fetch

The extension workflows build Pyrefly before packaging or testing the VS Code extension. A branch run hit a transient crates.io connection reset inside the actions-rust-cross cargo build step while fetching serde, which bypassed the retry wrapper because the fetch happened inside the third-party build action.

Fetch the Pyrefly Cargo dependencies explicitly through the local retry-command action before either the cross-compile action or native cargo build runs. For cross targets, include the matrix target in cargo fetch so target-specific dependencies are covered. This keeps the existing Rust cache useful on warm runs and gives cold or invalidated caches retry coverage before the expensive build step.

.github/workflows/build_extension.yml

diff --git a/.github/workflows/build_extension.yml b/.github/workflows/build_extension.yml
index 13d4c9d..99f7b30 100644
--- a/.github/workflows/build_extension.yml
+++ b/.github/workflows/build_extension.yml
@@ -126,6 +126,17 @@
       - name: set jemalloc page size for ARM64 macOS
         if: ${{ matrix.arch == 'arm64' && matrix.platform == 'darwin' }}
         run: echo "JEMALLOC_SYS_WITH_LG_PAGE=14" >> ${{ matrix.github_env }}
+      - name: Fetch Cargo dependencies
+        uses: ./.github/actions/retry-command
+        env:
+          RUST_TARGET: ${{ matrix.rust_target }}
+        with:
+          command: |
+            if [ -n "$RUST_TARGET" ]; then
+              cargo fetch --locked --manifest-path pyrefly/Cargo.toml --target "$RUST_TARGET"
+            else
+              cargo fetch --locked --manifest-path pyrefly/Cargo.toml
+            fi
       - name: build pyrefly binary (cross-compile)
         if: ${{ matrix.rust_target != '' }}
         uses: houseabsolute/actions-rust-cross@v1