Upgrade to psycopg 3

[jpmckinney]

Necessary changes:

• Change execute_values to executemany Alternatives to "psycopg2.extras.execute_values" and "psycopg2.extras.execute_batch" psycopg/psycopg#114
• Change cursor_factory=psycopg2.extras.DictCursor to row_factory=dict_row https://www.psycopg.org/psycopg3/docs/advanced/rows.html
• Review all other occurrences of psycopg2

I already made changes based on https://www.psycopg.org/psycopg3/docs/basic/from_pg2.html be5f4b2 087a5ff

Possible improvements:

• Use with block for connection
• Run connection.execute() for one-off statements
• Chain execute() and fetch*(), etc. https://www.psycopg.org/psycopg3/docs/basic/usage.html#shortcuts
• Consider connection pool across threads https://www.psycopg.org/psycopg3/docs/advanced/pool.html

Other advantages: server-side binding, prepared statements.

That said, most of our time is probably spent doing calculations in Python, not interacting with PostgreSQL, so not urgent.