Refactor out SQLAlchemy

[spwoodcock]

Issue

• Not everyone uses SQLAlchemy, but most will need to use a database driver.

Solution

• Replace SQLAlchemy with direct driver usage.
• psycopg2 is what SQLAlchemy uses underneath, and what most people generally use for connecting to Postgres.
  • There are many alternatives in the async world, as psycopg was quite slow to implement this.
  • But we will focus on a sync driver only for now (this doesn't require many queries / exceptional performance).

Context

This would improve the install of fmtm-splitter, reducing sub-dependencies.