Expose validation function for scripts not bundled with Vite

[aweebit]

I want the same environment variable loading and validation to happen in code bundled with Vite for SSR and before running command line tools such as kysely-ctl.

For the environment preloading, I use Node CLI's --import option like this:

node --import ./loadEnv.js node_modules/kysely-ctl/dist/bin.js

Right now, this is how my loadEnv.js file looks:

// @ts-check

import { ValidateEnv } from '@julr/vite-plugin-validate-env';

const { config } = ValidateEnv();
const configHandler = typeof config === 'function' ? config : config?.handler;
const envDefine = (
  await configHandler?.(
    { root: import.meta.dirname },
    { command: 'build', mode: 'development' },
  )
)?.define;
const env =
  envDefine &&
  Object.keys(envDefine).reduce((env, key) => {
    env[key.replace('import.meta.env.', '')] = JSON.parse(envDefine[key]);
    return env;
  }, {});

Object.assign(process.env, env);

It would be great if it could be simplified to something like this:

// @ts-check

import { validateEnv } from '@julr/vite-plugin-validate-env';

const env = await validateEnv(
  { root: import.meta.dirname },
  { command: 'build', mode: 'development' },
);

Object.assign(process.env, env);

I could submit a PR for this feature if you agree it's a reasonable addition to the library.