Export `run` function as a streamlined but flexible main entrypoint

Introduce a new assets.run entrypoint function that is:

Streamlined enough for us to generate into every new Hanami app
But flexible enough for users to provide arbitrary esbuild customisations

Here's what a default config/assets.mjs file would look like using this API:

import * as assets from "hanami-assets";

await assets.run();

And here's how it would look to add a custom esbuild plugin:

import * as assets from "hanami-assets";
import postcss from "esbuild-postcss";

await assets.run({
  esbuildOptionsFn: (args, esbuildOptions) => {
    const plugins = [...esbuildOptions.plugins, postcss()];

    return {
      ...esbuildOptions,
      plugins,
    };
  },
});

I've tested this exact config above in a real Hanami app and can confirm it actually works in terms of activating esbuild plugins.

In terms of code changes here, they are fairly wide-ranging. Sorry for the messy diff.

Let me guide you through the new landscape, however:

index.ts: defines the run function that serves as the main entry point, as shown above in those config/assets.mjs examples. This accepts an object of options so that they can all be optional.
args.ts: a new file that defines a proper interface and return object for the args that we parse when invoking node config/assets.mjs inside Hanami apps. This makes sure t things are nicely typed when passing an esbuildOptionsFn per the second example above.
esbuild.ts: defines our standard esbuild options, as used by the run function above. Most of the code here has been simply moved into a new location, otherwise left unchanged, aside from the new buildOptions and watchOptions functions that return the combined set of options for the two modes that we use.
esbuild-plugin.ts: defines our esbuild plugin. I've barely touched this file, except for a few light renames of its exports.

That really sums it up! If you spend most of your time checking out index.ts, args.ts and skimming esbuild.ts, you'll be up to speed with the changes.

There are a few other things I took care of while I was here:

Removed the config indicating that this package exposes an executable. Running via a config/assets.mjs script is now the one and only way to use this package.
Use Prettier for JS file linting/auto-formatting. This introduced a fair bit of churn, but I needed it because I wasn't sure how I should be formatting my TypeScript. 😆 And now's as good a time as any to get this into place.
Update TypeScript compilerOptions to use "module": "NodeNext". Per their relevant docs:

You very likely want "nodenext" for modern node projects.

For full context of how this will be used within a full Hanami app, see https://github.com/hanami/cli/pull/109.

hanami / assets-js

Export `run` function as a streamlined but flexible main entrypoint #10