Improve nthRoot handling for negative inputs

[pavanvamsi3]

Summary

• validate parameters for nthRoot
• return early on zero values
• handle odd roots of negative numbers by accounting for sign

Testing

• npm test

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https://chatgpt.com/codex/tasks/task_e_6844c3af04848333a6fe477d719df018

[Copilot]

Pull Request Overview

This PR improves the nthRoot function to handle negative inputs and validates parameters while preserving existing behavior. Key changes include:

• Adding basic parameter validation for n.
• Returning early for zero inputs.
• Handling odd roots of negative numbers by accounting for the sign and applying an iterative Newton–Raphson approach for other cases.

[Copilot]

[nitpick] Consider simplifying the conversion chain by either directly returning result.toPrecision(6) for consistency with the earlier branches or clearly documenting the need for converting to a Number then back to a String.

Suggested change

	return Number(result.toPrecision(6)).toString();
	return result.toPrecision(6);