fix: add __main__.py so python -m directdnsonly works in container 🐛

- directdnsonly/__main__.py: inserts package dir into sys.path before
  importing main.py (which uses short-form relative imports) then calls
  main(); works for both `python -m directdnsonly` and the dadns script
- pyproject.toml: wire up `dadns` console script entry point

pyproject.toml

@@ -20,6 +20,9 @@ dependencies = [
     "requests (>=2.32.0,<3.0.0)",
 ]
 
+[project.scripts]
+dadns = "directdnsonly.__main__:run"
+
 [tool.poetry]
 package-mode = true