Pipeline: Fix CAWP error with terms ending in early January

[benhammondmusic]

Description and Motivation

• fixes issue where CAWP was only listing women in the full year they served, but our code for extracting denominators for US Congress was counting the last few days of people's terms, (january 1-3) and including that year in the denominator calculations. this resulted in the weird "bumpiness" of the chart, which is now fixed
• adds usecols to speed up loading of giant csv file

Has this been tested? How?

• tests passing

Screenshots (if appropriate)

OLD DATA LEFT / NEW MORE ACCURATE DATA RIGHT

Types of changes

(leave all that apply)

• Bug fix

New frontend preview link is below in the Netlify comment 😎