style: apply cargo fmt and add formatting check to CI (#319)

Runs `cargo fmt --check` in the rust_crate CI action to catch
formatting issues before they land.

.github/actions/rust_crate/action.yaml

@@ -13,6 +13,11 @@ inputs:
 runs:
   using: "composite"
   steps:
+    - name: Check Formatting
+      working-directory: ${{ inputs.working_directory }}
+      shell: ${{ inputs.shell }}
+      run: cargo fmt --check
+
     - name: Clippy
       working-directory: ${{ inputs.working_directory }}
       shell: ${{ inputs.shell }}