Fix cooldown duration variance calculation

[dobshn]

Changes

• Fixed duration calculation in reset() method.
• Previously, Math.random() was multiplied by milliseconds + variance, which caused incorrect variance handling.
• Now correctly uses variance * 2 to randomize duration between (milliseconds - variance) and (milliseconds + variance).

Why

• Ensures the cooldown duration properly reflects the intended variance range.

Please let me know if any changes are needed.
Thank you! 😀