feat: migrate to ESM

[CMCDragonkai]

Description

Migrate to ESM.

Issues Fixed

• Related https://github.com/MatrixAI/TypeScript-Demo-Lib/issues/32

Final checklist

• [x] Domain specific tests
• [x] Full tests
• [x] Updated inline-comment documentation
• [x] Lint fixed
• [x] Squash and rebased
• [x] Sanity check the final build

[CMCDragonkai]

The ts-custom-error package actually produces CJS and ESM, switching over didn't require any changes.