Replace `G` with `B` for billions in plot money formatting

[griff-rees]

This is a longstanding issue with d3-format. See

• enable formatting numbers with natural language suffixes, k(ilo), M(illion), B(illion) plotly/plotly.js#6091
• Implement Binary prefix, Currency prefix (Merge #70 #81) d3/d3-format#96
• https://stackoverflow.com/questions/68005050/b-billions-instead-of-g-giga-in-python-plotly-customdata-si-prefix-d3