Remove dependency on testify/assert

[paked]

Looking at our mod file, we currently depend on testify/assert (and then it depends on another library) -- it seems we only actually use testify for some deep-equal checks in messenger_test.go.

I'd prefer it if we just wrote our own functions for this behavior in order to eliminate any dependencies we don't actually need.

[OAyomide]

I see

I'd love to give it a shot. I'll get on it shortly.