Consider updating JSBI to a newer version

[marktoda]

They are on major 4 now: https://github.com/GoogleChromeLabs/jsbi/blob/main/package.json. Some downstream packages are beginning to require higher versions than the one we are using; so we should consider upgrading. I imagine it will have a few breaking changes that we'll have to work through

[hensha256]

Also maybe worth just dropping altogether and using native bigint instead of adding v4 support