onSuccess async function in tsup.config.ts should wait until tsc has ran

[alii]

I need to copy some some files (namely copy .d.ts to .d.cts) and can't because tsup runs the onSuccess function inside the config file before tsc has had a chance to finish compiling types. It would make sense to run this after.

Also, the function is called onSuccess but there are plenty of reasons why tsc might fail at this point, meaning that onSuccess has ran even on failure.

My reasoning for this is for esm/cjs compatibility. Eventually it would be cool if tsup could properly spit out the correct files, but I'm having somewhat of a difficult time understanding what the correct should be anyway. JS ecosystem 😅

[alii]

Closing as duplicate of #700