Speed up GitHub Actions tests with parallelization (#3107)

- Add pytest-xdist and pytest-split to dev dependencies for parallel test execution
- Split tests into 8 parallel groups per Python version for better distribution
- Enable CPU-level parallelization with -n auto to maximize resource usage
- Add fail-fast strategy and maxfail=3 to stop early on failures
- Add job name to match branch protection rules
- Reduce test timeout from default to 30s for faster failure detection
- Remove redundant cache configuration

pyproject.toml

@@ -83,6 +83,8 @@ dev-dependencies = [
     "pytest-recording>=0.13.2",
     "pytest-randomly>=3.16.0",
     "pytest-timeout>=2.3.1",
+    "pytest-xdist>=3.6.1",
+    "pytest-split>=0.9.0",
 ]
 
 [project.scripts]