Miscellaneous hackathon fixes

[aschampion]

This fixes a few failing tests, some of the louder typechecking noise in my env, and aims to make get a dev env setup a bit smoother.

• README: adapt dev instructions for zsh-like shells
• pytest: ignore submodule on missing k3d dep
• smat: fix non-match iterations
• smat: replace with valid type hint
• Add minimal editorconfig

[schlegelp]

Hi @aschampion. Are you happy with merge this or is this still WIP?

[aschampion]

This is ready to merge, any further fixes are mixed in with the executor refactor that I'll PR later.