Workspaces/Submodules: top-level `pnpm i` doesn't install deps of protobuf.js

Gotta move `packages/cosmjs-esm/protobuf.js` to `packages/protobuf.js` but then `cosmjs-esm` becomes dependent on the workspace. But... there is already a similar case in `toolbox`/`ensuite`/`ubik`, so might as well. (Gotta try first if adding protobuf to `/pnpm-workspace.yaml` won't work on a fresh checkout though.)