Replace lerna, yarn with npm builtins

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In the past few years, lerna has become more deprecated, and npm workspace support has improved to the point where I think we can do everything needed without other software.

https://stackoverflow.com/questions/64909635/is-lerna-needed-anymore-with-npm-workspaces
https://tyhopp.com/notes/replacing-lerna
https://betterprogramming.pub/lerna-is-officially-dead-long-live-monorepos-9853c80a7b0e

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Also, in the spirit of keeping things simple, planning to
replace jest with just using the builtin node test runner , and
replace prettier with just writing pretty code.