Simplify the pkg.json scripts

[louisinger]

• not sure we need two folders for sources, let's only have ts_src with Typescript sources and drop the duplicate src sources ? The JS files should be generated while we build typescript (in a dist folder) -> similar to what's tsdx do. cc @tiero <- NACK
• ideally, scripts should be only yarn test, yarn build and yarn format.

Doing that change will be a huge "fork" comparing to bitcoinjs but should be ok to merge next bitcoinjs changes if we keep ts_src and then use our own build process to generate JS files

[tiero]

nack for dropping the src folder. The BitcoinJS reason is auditability.

[altafan]

Can this be closed? @tiero @louisinger