[Feat][Js] Make ai.generateStream no longer require a double await

[inlined]

Fixes #1593

Rewrote generateStream so you longer need to call await to get the return value of objects that are themselves async.

As a style change I named the struct for {resolve, reject, promise} as Task because that's how I've commonly seen this design called.

The former method for passing into an async generator was a bit fragile because it depended on the exact order of the callbacks to the run loop (in fact, in my refactoring I broke it). Instead I created a buffering utility class called Channel<T>, inspired by Go channels but implements AsyncIterable for receiving.

I've had to change the copyright script from ts-node to tsx in many of my PRs because I get import vs require errors trying to load child-process. Since tsx is more officially supported I decided to change the way the script runs rather than adding module resolution annotations.

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (unit tested, including new test)
• Docs updated (updated jsdocs)