Convert to ESModules & export everything

[NatoBoram]

Hi!

While using this package, I needed to import some private types. There were also some imports that were very tricky to use, so I moved the package to ESModules for better compatibility. I also encountered an issue while using Jest; it seems like it's severely outdated as its ESModule support is experimental. Switching to Vitest made it work without having a config file.

With this change, instead of:

import type {
	FunctionDef,
	ObjectProp, // Module '"openai-chat-tokens/dist/functions.js"' declares 'ObjectProp' locally, but it is not exported.
} from "openai-chat-tokens/dist/functions.js"

It's now:

import type { FunctionDef, ObjectProp } from "openai-chat-tokens"

• Closes Convert to ESModules & export everything coderabbitai/openai-chat-tokens#1

[hellohejinyu]

import { functionsTokensEstimate } from 'openai-chat-tokens';

type FunctionDef = Parameters<typeof functionsTokensEstimate>[0][number];
type ObjectProp = FunctionDef['parameters'];

Maybe you can try like this.

[NatoBoram]

Yeah, that's true. I ended up re-publishing the package under https://github.com/coderabbitai/openai-chat-tokens to avoid dealing with more type aliases.