Reorganize rust crates into a flat crates directory, simplify some CI steps (#4496)

* Move all rust crates (except lib) into crates dir, w/o nesting

* Remove stale path from .gitattributes

* Rename lib.rs files for easier navigation

* Rename mod.rs file for easier navigation

* Fix emscripten-version path

* Fix fixtures dir paths

* Use the default rustfmt settings

* Don't use nightly on CI

.github/workflows/build.yml

@@ -73,7 +73,7 @@ jobs:
       uses: actions/checkout@v4
 
     - name: Read Emscripten version
-      run: printf 'EMSCRIPTEN_VERSION=%s\n' "$(<cli/loader/emscripten-version)" >> $GITHUB_ENV
+      run: printf 'EMSCRIPTEN_VERSION=%s\n' "$(<crates/loader/emscripten-version)" >> $GITHUB_ENV
 
     - name: Install Emscripten
       if: ${{ !matrix.no-run && !matrix.use-cross }}

.github/workflows/ci.yml

@@ -34,22 +34,11 @@ jobs:
           toolchain: stable
           components: clippy, rustfmt
 
-      - name: Set up nightly Rust toolchain
-        uses: actions-rust-lang/setup-rust-toolchain@v1
-        with:
-          toolchain: nightly
-          components: clippy, rustfmt
-
       - name: Lint files
         run: |
           make lint
           make lint-web
 
-      - name: Lint files (Rust nightly)
-        continue-on-error: true
-        run: |
-          make lint-nightly
-
   sanitize:
     uses: ./.github/workflows/sanitize.yml