Add pytest-timeout

Pytest complains that 'timeout' is not a valid key. Adding the
'pytest-timeout' package fixes that.

pyproject.toml

@@ -45,6 +45,7 @@ test = [
     "pytest-cov",
     "pytest-socket",
     "pytest-leaks",
+    "pytest-timeout",
     "pympler",
 ]
 check = [