Remove the `mergestat/mergestat-lite` dependency

[patrickdevivo]

• This is a fairly big task. The context is that we use mergestat/mergestat-lite (the CLI) as a library in the Fuse worker so that we can run SQL (SQLite virtual table) queries to fetch data from Git and GitHub, and then insert into Postgres. This was done so as not to duplicate API integration code - but it resulted in a very messy and odd setup, because using mergestat/mergestat-lite as a library is pretty difficult (the SQLite dependence makes things weird)…that’s the main motivation - we can clean up the codebase a great deal (at the expense of re—integrating more API client code) and simplify a lot of things
• This would require implementing a GitHub API client (to do things like pagination, rate limit handling, etc)