Determine test plan

[rainest]

Existing deck integration tests generally rely on the CLI. This repo will not have that CLI readily available, and will need some changes to its testing strategy.

Offhand, I'd expect the simplest option is have the test actions here check out a copy of the deck repo main, update its go.mod to use the PR head commit as the current version of this library, and run deck's usual test suite. This approach will probably hit chicken-egg problems where coverage for this repo relies on features that aren't yet merged into deck main. Unsure how to best handle that, but we can maybe add a variant of tests that lets you choose the downstream branch and still satisfies the same Actions status.

[rainest]

#10 is the most basic option for this. It reuses existing tests by importing deck as a test dependency here.

This generally works, though creates a (test only) dependency chain that's a bit silly. To avoid it we'd need to implement some sort of alternate to the client code, that invokes the sync/diff functions here without either of the downstream consumers (deck and KIC) of this library.