chore: upstream sync v4 (48 commits) + CI workflow

.github/workflows/test.yml

@@ -0,0 +1,33 @@
+name: tests
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.11", "3.12"]
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install ".[dev]"
+
+      - name: Run tests
+        run: |
+          python -m pytest tests/ \
+            --ignore=tests/test_matrix_channel.py \
+            -q --tb=short