ci: aggiungi job test con pytest e codecov, build dipende da test

- job test: pytest --cov su ubuntu-latest python 3.12, upload coverage codecov
- job build: needs test, gira solo dopo test passati
- trigger: push+PR su src/** tests/** pyproject.toml

Author: Gabrymi93

.github/workflows/build-context.yml

@@ -10,9 +10,38 @@ on:
     paths:
       - 'dataciviclab.config.yml'
       - 'src/**'
+      - 'tests/**'
+      - 'pyproject.toml'
+  pull_request:
+    paths:
+      - 'src/**'
+      - 'tests/**'
+      - 'pyproject.toml'
 
 jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v6
+
+      - uses: actions/setup-python@v6
+        with:
+          python-version: '3.12'
+
+      - name: Install
+        run: pip install -e ".[dev]"
+
+      - name: Test
+        run: pytest --cov=src/agent_context_builder --cov-report=xml
+
+      - name: Upload coverage
+        uses: codecov/codecov-action@v4
+        with:
+          fail_ci_if_error: false
+
   build:
+    needs: test
     runs-on: ubuntu-latest
     permissions:
       contents: write