feat(vite-dev-server): migrate to async fs operations for better perf…

[lucgonp]

…ormance

• Replace fs.readFileSync with async fs.readFile
• Add proper error handling with debug logs
• Improve performance by avoiding event loop blocking
• Remove TODO comment about async fs methods

This follows Node.js best practices and improves DX with faster build times.

• Closes

Additional details

Steps to test

How has the user experience changed?

PR Tasks

• Have tests been added/updated?
• Has a PR for user-facing changes been opened in cypress-documentation?
• Have API changes been updated in the type definitions?

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Note

Switches to async file reads, adds cached init loader with error-handled loading, and injects it into transformed index.html.

• Vite dev server plugin (npm/vite-dev-server/src/plugins/cypress.ts):
  • Replace sync fs.readFileSync and fs.promises.readFile with fs/promises.readFile imports/usage.
  • Add async loadInitFile with debug logging and error handling; introduce cached loaderPromise via getLoaderPromise.
  • transformIndexHtml: read index.html asynchronously and inject loader content via await getLoaderPromise().
  • Remove obsolete TODO about async fs methods.

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