[javascript] Add es module build

[arjunyel]

Motivation

Creating an ES Module build allows ESM environments to treeshake the svix library

Solution

Created both a CJS and ESM build using tsup. Also updated all dependencies, upgraded to the Eslint v9 config, and switched from Jest to Vitest.

Based on top of #1162

[tasn]

Thanks for the contribution, this is a great addition!

Were the changes to eslint and prettier (moving to a different format) necessary? Also, I'm less familiar with tsup, is this what people use nowadays?

[arjunyel]

Happy to help, thanks for making Svix :D

The eslint changes were necessary as the old configuration format is being removed.

To make npm packages I personally use dnt which lets you create both a Deno native and npm native packages. An example is I used it to make Lago's SDK. The downside it requires Deno while this repo already uses node.

For node projects tsup is the best tool I've found, here's a video of TypeScript expert Matt Pocock talking about it.