feat: add module entrypoint

small useless feature, but the application can now be run with python -m
ahriman

ahriman-core/tests/ahriman/test_main.py

@@ -0,0 +1,15 @@
+import runpy
+
+from pytest_mock import MockerFixture
+
+
+def test_main(mocker: MockerFixture) -> None:
+    """
+    must run the application and exit with its status
+    """
+    run = mocker.patch("ahriman.application.ahriman.run", return_value=42)
+    exit_mock = mocker.patch("sys.exit")
+
+    runpy.run_module("ahriman", run_name="__main__")
+    run.assert_called_once_with()
+    exit_mock.assert_called_once_with(42)