chore: rm ts-jest and almost all jest config files

[franklevasseur]

really big simplification of jest configurations

Basically, if you run yarn test at root of repo, you run jest on the packages/ directory on *.js files.

If you run yarn test inside a specific package, you run jest on dist/ directory also on on *.js files.

No need to transpile *.ts test files with babel or ts-jest. Just build the test and run it afterward.

Tests are now way faster and easier to debug using sourceMaps: true.