ci: parallelize integration suite with pytest-xdist; fast PR gate + full coverage on merge

- Add pytest-xdist to the CI Dockerfile (image -> v10).
- Worker-isolate TEST_DATA_DIR (PYTEST_XDIST_WORKER) so concurrent xdist
  workers never collide on shared-filesystem fixtures.
- Register a 'ci' marker and tag a fast representative subset of integration
  tests (basic TCP, incremental, compression, delete, basis, append).
- ci.yaml: lint + build + unit + the marked subset (-n4) on every PR; the
  full integration suite plus sanitizer/fuzz/coverage/valgrind run only on
  push to dev/main.
- Integration step runtime drops from ~860s (serial) to ~230s (-n4); the PR
  gate lands well under ~3 minutes.

.gitea/workflows/ci.yaml

@@ -8,7 +8,7 @@ on:
 jobs:
   lint:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v9
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -19,9 +19,13 @@ jobs:
       - name: cppcheck
         run: cppcheck --enable=warning,style,performance,portability --suppress=missingIncludeSystem --error-exitcode=1 --inline-suppr src/ tests/
 
+  # Fast PR gate: build + unit tests + a representative subset of integration
+  # tests (marked `ci`), parallelized with pytest-xdist.  Only the full coverage
+  # jobs below (sanitizers/fuzz/coverage/valgrind and the FULL integration
+  # suite) run on merge to dev/main, so PR CI stays well under ~3 minutes.
   build-and-test:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v9
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
     needs: lint
     steps:
       - name: Checkout
@@ -36,13 +40,19 @@ jobs:
       - name: Unit Tests
         run: ctest --test-dir build --output-on-failure -j$(nproc)
 
-      - name: Integration Tests
-        run: python3 -m pytest tests/integration/ -v --tb=short
+      - name: Integration Tests (PR smoke subset)
+        if: github.event_name == 'pull_request'
+        run: python3 -m pytest tests/integration/ -n 4 --dist=loadgroup -m ci --durations=25 --tb=short -q
+
+      - name: Integration Tests (full suite)
+        if: github.event_name == 'push'
+        run: python3 -m pytest tests/integration/ -n 4 --dist=loadgroup --durations=25 --tb=short -q
 
   sanitizers:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v9
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
     needs: lint
+    if: github.event_name == 'push'
     strategy:
       matrix:
         sanitizer: [address, undefined]
@@ -61,8 +71,9 @@ jobs:
 
   fuzz-build:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v9
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
     needs: lint
+    if: github.event_name == 'push'
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -82,8 +93,9 @@ jobs:
 
   coverage:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v9
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
     needs: lint
+    if: github.event_name == 'push'
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -105,8 +117,9 @@ jobs:
 
   valgrind:
     runs-on: ubuntu-latest
-    container: gitea.tap-tap.win/taptap/fastsync-ci:v9
+    container: gitea.tap-tap.win/taptap/fastsync-ci:v10
     needs: lint
+    if: github.event_name == 'push'
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -120,4 +133,4 @@ jobs:
       - name: Valgrind Memcheck
         run: valgrind --leak-check=full --show-leak-kinds=definite --error-exitcode=1 ./build/tests
         env:
-          FASTSYNC_UNDER_VALGRIND: "1"
+          FASTSYNC_UNDER_VALGRIND: "1"