test: run pytest in parallel with pytest xdist (#1319)

Distributing tests across multiple CPUs to speed up test execution.

tox.ini

@@ -64,7 +64,21 @@ commands =
     pyright {posargs}
 
 [testenv:unit]
-description = Run unit tests
+description = Run unit tests in parallel without coverage
+passenv =
+    RUN_REAL_PEBBLE_TESTS
+    PEBBLE
+deps =
+    PyYAML==6.*
+    websocket-client==1.*
+    pytest~=7.2
+    pytest-xdist~=3.6
+    typing_extensions~=4.2
+commands =
+    pytest -n auto --ignore={[vars]tst_path}smoke -v --tb native {posargs}
+
+[testenv:coverage]
+description = Run unit tests with coverage
 passenv =
     RUN_REAL_PEBBLE_TESTS
     PEBBLE