feat(dev-server): introduce env

[yusukebe]

This PR introduces the concept of ENV and the env option.

For Cloudflare Pages, the current cf option allows us to use bindings. For example:

export default defineConfig({
  plugins: [
    devServer({
      entry: 'src/index.ts',
      cf: {
        bindings: {
          NAME: 'Hono',
        },
      },
    }),
  ],
})

With this configuration, we can access variables through c.env:

app.get('/', (c) => {
  return c.text(c.env.NAME)
})

This is currently exclusive to Cloudflare Pages, but in the future, it may be extended to other runtimes/platforms with specific environment values. While c.env seems to be used for Cloudflare, other platforms/runtimes may also use bindings/c.env. For instance, the AWS Lambda adapter currently uses env:

https://github.com/honojs/hono/blob/main/src/adapter/aws-lambda/handler.ts#L126-L143

This PR suggests separating the Cloudflare Pages-specific functionality from dev-server.ts. With this change, the getEnv() method for Cloudflare Pages is placed in cloudflare-pages/index.ts, and users can include the env in their vite.config.ts:

import { getEnv } from '@hono/vite-dev-server/cloudflare-pages'

// ...

export default defineConfig({
  plugins: [
    devServer({
      env: getEnv({
        bindings: {
          NAME: 'Hono',
        },
      }),
    }),
  ],
})

With this mechanism, adding support for another platform that uses environment variables becomes straightforward:

import { getEnv } from '@hono/vite-dev-server/another-one'

// ...

export default defineConfig({
  plugins: [
    devServer({
      env: getEnv({
        someFunction: {
          NAME: 'Hono',
        },
      }),
    }),
  ],
})

[yusukebe]

Hey @Code-Hex !

Could you review this?

[Code-Hex]

Looks great to me 😁

[changeset-bot]

🦋 Changeset detected

Latest commit: 1e7f4ae

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@hono/vite-dev-server	Minor

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[yusukebe]

@Code-Hex

Thanks for reviewing. Let's go with this!