Fix tests, update holochain client, alter build output

[mattyg]

I was going to merge the 3 prior prs below into one, but ended up just merging the 2 drafts that I kept open.

I switched back to using webpack and modified its config to output an es module instead of cjs.

Resolves #115

• replace vite with vitest
• fix test mocking
• fix failing tests
• bump holochain client to 0.16.3 (and remove node 16.x CI support)
• bump webpack deps
• switch to es module output, instead of commonjs

[mattyg]

okay this is actually ready @robbiecarlton

[robbiecarlton]

Thanks for this @mattyg - awesome work!

I'm closing this PR as I had to create a new branch to resolve merge conflicts