use flit for packages.

.github/workflows/ci.yml

@@ -36,10 +36,6 @@ jobs:
         # actual=`readlink -f /usr/bin/mecab`
         # ldd $actual
 
-    - name: Extra dev deps
-      if: matrix.python_version == '3.13'
-      run:  sudo apt-get install -y build-essential python3-dev
-
     - uses: actions/checkout@v4
       with:
         submodules: true
@@ -49,7 +45,12 @@ jobs:
         python-version: ${{ matrix.python_version }}
         cache: 'pip' # caching pip dependencies
 
-    - run: pip install -r requirements-dev.txt
+    - name: Install packages using flit
+      run: |
+        pip install flit
+        # --only-deps: Installs only the dependencies, not Lute itself
+        # --deps develop: both regular and optional dependencies.
+        flit install --only-deps --deps develop
 
     - name: Setup config
       run: |