ci: replace unsupported artifact sharing with a bind-mounted uv cache

The self-hosted act_runner doesn't support upload/download-artifact, so drop
that plumbing and instead run jobs in an explicit container with a persistent
host directory mounted at /uv-cache (UV_CACHE_DIR), backed by valid_volumes on
the runner. uv sync still runs per job but hits a warm local cache instead of
re-downloading/building packages every time.

.gitea/workflows/ci.yml

@@ -7,80 +7,61 @@ name: CI
   pull_request:
     branches: [master]
 
-jobs:
-  setup:
-    name: Setup environment
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - uses: astral-sh/setup-uv@v5
-        with:
-          enable-cache: true
-      - run: uv sync --extra cpu --extra dev
-      - run: tar -czf venv.tar.gz .venv
-      - uses: actions/upload-artifact@v4
-        with:
-          name: venv
-          path: venv.tar.gz
+env:
+  UV_CACHE_DIR: /uv-cache
 
+jobs:
   ruff-check:
     name: Lint (ruff check)
-    needs: setup
     runs-on: ubuntu-latest
+    container:
+      image: docker.gitea.com/runner-images:ubuntu-latest
+      volumes:
+        - /srv/act-runner-cache/uv:/uv-cache
     steps:
       - uses: actions/checkout@v4
       - uses: astral-sh/setup-uv@v5
-        with:
-          enable-cache: true
-      - uses: actions/download-artifact@v4
-        with:
-          name: venv
-      - run: tar -xzf venv.tar.gz
+      - run: uv sync --extra cpu --extra dev
       - run: uv run ruff check .
 
   ruff-format:
     name: Format (ruff format)
-    needs: setup
     runs-on: ubuntu-latest
+    container:
+      image: docker.gitea.com/runner-images:ubuntu-latest
+      volumes:
+        - /srv/act-runner-cache/uv:/uv-cache
     steps:
       - uses: actions/checkout@v4
       - uses: astral-sh/setup-uv@v5
-        with:
-          enable-cache: true
-      - uses: actions/download-artifact@v4
-        with:
-          name: venv
-      - run: tar -xzf venv.tar.gz
+      - run: uv sync --extra cpu --extra dev
       - run: uv run ruff format --check .
 
   type-check:
     name: Type check (ty)
-    needs: setup
     runs-on: ubuntu-latest
+    container:
+      image: docker.gitea.com/runner-images:ubuntu-latest
+      volumes:
+        - /srv/act-runner-cache/uv:/uv-cache
     steps:
       - uses: actions/checkout@v4
       - uses: astral-sh/setup-uv@v5
-        with:
-          enable-cache: true
-      - uses: actions/download-artifact@v4
-        with:
-          name: venv
-      - run: tar -xzf venv.tar.gz
+      - run: uv sync --extra cpu --extra dev
       - run: uv run ty check .
 
   test:
     name: Tests
-    needs: [setup, ruff-check, type-check]
+    needs: [ruff-check, type-check]
     runs-on: ubuntu-latest
+    container:
+      image: docker.gitea.com/runner-images:ubuntu-latest
+      volumes:
+        - /srv/act-runner-cache/uv:/uv-cache
     steps:
       - uses: actions/checkout@v4
       - uses: astral-sh/setup-uv@v5
-        with:
-          enable-cache: true
-      - uses: actions/download-artifact@v4
-        with:
-          name: venv
-      - run: tar -xzf venv.tar.gz
+      - run: uv sync --extra cpu --extra dev
       - run: uv run pytest
 
   sync-version-on-tag: