Completely remove underscore dependency and migrate to ES6+ features with performance focus

[wreiske]

The project currently relies on the underscore library for various utilities. With the capabilities of modern ES6+ JavaScript, we can replace underscore's functionality using built-in methods, potentially improving maintainability and performance.

This issue covers:

• Identifying all usages of underscore throughout the codebase
• Refactoring code to use native ES6+ JavaScript features instead of underscore
• Ensuring that performance is not negatively impacted—in fact, where possible, improve performance by using optimal built-in methods
• Removing underscore from the dependency list and ensuring all references are cleaned up
• Adding or updating tests to confirm correctness and performance of the refactored code

Acceptance Criteria:

• No underscore imports or references remain in the codebase
• All functionality previously provided by underscore is handled with native JavaScript
• Performance of critical code paths is measured and documented, with improvements where possible
• All tests pass after migration