tests: add pytest-xdist for parallel test execution

.cspell/library_terms.txt

@@ -152,6 +152,7 @@ vars
 viewcode
 vmap
 vmaps
+worksteal
 writebytes
 xlabel
 ylabel

.github/workflows/coverage.yml

@@ -47,7 +47,7 @@ jobs:
       - name: Debug - uv pip freeze
         run: uv pip freeze
       - name: Assess coverage of unit tests
-        run: uv run pytest tests/unit --cov
+        run: uv run pytest tests/unit -n auto --dist worksteal --cov
       - name: Extract total coverage percentage
         id: cov
         run: |

.github/workflows/unittests.yml

@@ -58,10 +58,10 @@ jobs:
     - name: Debug - uv pip freeze
       run: uv pip freeze
     - name: Test with pytest
-      run: uv run pytest --ignore=tests/integration
+      run: uv run pytest --ignore=tests/integration -n auto --dist worksteal
     # Integration tests are slow, so only run if all other tests pass.
     - name: Test integration tests
-      run: uv run pytest tests/integration
+      run: uv run pytest tests/integration -n auto --dist worksteal
     - name: Minimize UV cache
       run: uv cache prune --ci
       if: always()

pyproject.toml

@@ -66,6 +66,7 @@ test = [
     "pytest>=8",
     "pytest-cov>=6",
     "pytest-rerunfailures>=15",
+    "pytest-xdist>=3",
     "scipy>=1.13",
 ]
 # Compile documentation