feat: Another copy command implementation

[pnadolny13]

FWIW I also had a draft for using COPY similar to #370. It worked for me and was significantly faster but I havent tested enough to say its ready to merge. I based it off of the transferwise logic https://github.com/transferwise/pipelinewise-target-postgres/blob/bef5a2786afab3c1600e62a77b6d121625e7bc8e/target_postgres/db_sync.py#L357.

Without reviewing in more detail I dont know if this or #370 is a better approach. I'm happy with either as long as we get the performance improvement 😄 . I wanted to open this to share another implementation if its helpful in getting to the final solution.

cc @kinghuang

[kinghuang]

Nice! The biggest difference that I see is that using csv.DictWriter will just serialize values by str(), which won't handle things like None (null), arrays of jsonb, and other complex types correctly for transmission to PostgreSQL. Most of my code deals with the serialization process to CSV. I also prepare the stream data in memory instead of writing to a temporary file.

[pnadolny13]

@kinghuang thanks for explaining the differences!

The biggest difference that I see is that using csv.DictWriter will just serialize values
Great! Yeah this seems like a more robust approach.

I also prepare the stream data in memory instead of writing to a temporary file.
I wonder which approach is better. I guess writing to disk is likely more memory efficient but is a little slower. I wonder what copy_expert is doing with the input behind the scenes.

[pnadolny13]

I'll close this draft though in favor of #370