feat: avoid Vite transforms for non-vite projects

[sheremet-va]

Description

This PR adds a new option to use Node Loaders without relying on Vite transforms at all.

Related #7200
Related #2841

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[ffMathy]

This is great. Should it be default for Node versions 23.6 and later?

[sheremet-va]

const config = {
  test: {
    loader: '../my-loader.js'
  }
}

// works in test thread
const loader = importLoader('custom-file')
loader.import('custom-env')

// works on the server
const server = {
  loadCoverageProvider() {
    const loader = importLoader()
    loader.import('file')
  }
}