Refactor CommonJS syntax (require) to ES Module syntax

[gerteck]

Please confirm that you have searched existing issues in the repo

Yes, I have searched the existing issues

Any related issues?

This is a sub issue and blocker for #2615

What is the area that this feature belongs to?

Code Quality

Is your feature request related to a problem? Please describe.

We are currently using legacy CommonJS syntax (require/module.exports) throughout the project. While this works with our current build configuration, it is creating significant technical debt and blocking our migration to ES Modules (ESM).

• Ultimately we want to switch our build output to native ES Modules (ESM) to support modern environments and tree-shaking.
  • However, TypeScript does not automatically rewrite CommonJS runtime syntax such as require and module.exports. If we emit ESM without first refactoring these usages to import/export, the generated code will fail at runtime because require is not available in native ESM.
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Describe the solution you'd like

Standardize on the ES Module syntax (import / export) immediately. Decouples the syntax migration from the configuration migration, allowing us to safely adopt modern syntax now while maintaining our current build pipeline.

1. Refactor Syntax: Systematically replace require statements with import statements.
2. Add Type Definitions: Create local .d.ts files for untyped dependencies to ensure the new import syntax is fully typed. (Need to find a suitable place and configs appropriately)

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Describe alternatives you've considered

No response

Additional context

No response

[gerteck]

Example of required changes for legacy libraries (e.g., fastmatter):

Before:

const fastmatter = require('fastmatter'); // Untyped, CJS syntax

After:

// src/@types/fastmatter.d.ts need to be created
import fastmatter from 'fastmatter'; // Typed, ESM syntax

The careful part is where to add custom type definitions since these are relatively old packages not maintained, need to either find alternative packages, directly in-house the code etc.