feat: migrate from Forgejo to GitLab CI with test reporting

- Convert Forgejo workflow to GitLab CI/CD (.gitlab-ci.yml) - Add JUnit XML and coverage reporting
with pytest-cov - Configure caching and artifacts for better CI performance - Fix pytest.ini
configuration and enhance .coveragerc - Support GitLab v18.1.1 with comprehensive test visualization

.gitlab-ci.yml

@@ -0,0 +1,36 @@
+# GitLab CI/CD pipeline for doi2dataset
+# Compatible with GitLab v18.1.1
+
+stages:
+  - test
+
+variables:
+  PIP_CACHE_DIR: "$CI_PROJECT_DIR/.cache/pip"
+
+cache:
+  paths:
+    - .cache/pip/
+    - .venv/
+
+test:
+  stage: test
+  image: python:3
+  before_script:
+    - python -m pip install --upgrade pip
+    - pip install -r requirements.txt
+    - pip install -r requirements-dev.txt
+  script:
+    - pytest
+  artifacts:
+    reports:
+      junit: junit.xml
+      coverage_report:
+        coverage_format: cobertura
+        path: coverage.xml
+    paths:
+      - htmlcov/
+    expire_in: 1 week
+  coverage: '/(?i)total.*? (100(?:\.0+)?\%|[1-9]?\d(?:\.\d+)?\%)$/'
+  only:
+    - branches
+    - merge_requests