chore: declare napalm-device-types, stop tracking build artefacts

pyproject.toml did not list napalm-device-types although the code
imports it (CI installed it by hand); it now requires 4.13, whose fix
templates the next commit uses. Seven .pyc and six egg-info files were
tracked; they go, and a .gitignore keeps them out.

Closes #11

.gitignore

@@ -0,0 +1,6 @@
+__pycache__/
+*.pyc
+*.egg-info/
+.venv/
+build/
+dist/