feat: run pytest in parallel with pytest-xdist by default

- Add pytest-xdist to the dev group and regenerate uv.lock
- Pass --numprocesses=auto through [tool.pytest] addopts so every pytest
  invocation, local or CI, distributes tests across all CPU cores

Author: mjun0812

template/pyproject.toml

@@ -22,7 +22,14 @@ build-backend = "hatchling.build"
 packages = ["src/{{package_name}}"]
 
 [dependency-groups]
-dev = ["prek>=0.5.2", "pytest>=9.1.1", "pytest-cov>=7.1.0", "ruff>=0.16.6", "ty>=0.0.78"]
+dev = [
+    "prek>=0.5.2",
+    "pytest>=9.1.1",
+    "pytest-cov>=7.1.0",
+    "pytest-xdist>=3.8.0",
+    "ruff>=0.16.6",
+    "ty>=0.0.78",
+]
 
 [tool.ruff]
 line-length = 100
@@ -82,7 +89,7 @@ convention = "google"
 
 [tool.pytest]
 testpaths = ["tests"]
-addopts = ["-ra", "--strict-markers", "--strict-config"]
+addopts = ["-ra", "--strict-markers", "--strict-config", "--numprocesses=auto"]
 xfail_strict = true
 
 [tool.coverage.run]