test(python-generator): update tests to do not assume src/ directories

Updated tests to do not implicitly assume a 'src/' directory structure
and removed all 'src/' subdirectory structures in test project
directories (if possible).

tests/unit/cli/python_project/project/pkg/module.py

@@ -0,0 +1,11 @@
+def f(a: int = 42) -> str:
+    """
+    Does something.
+
+    :param a: A parameter.
+    :type a: int
+
+    :return: A string.
+    :rtype: str
+    """
+    ...