♻️ Refactoring

• Core: Refactored Spectrum struct to remove Copy trait, forcing explicit data flow and improving performance by avoiding expensive implicit copies.
• Core: Improved numerical stability in new_blackbody and integrate_product functions within spectral.rs, ensuring physical consistency and preventing potential overflows.
• Core: Replaced implicit amplitude scaling with new_gaussian_normalized to guarantee energy conservation in spectral modeling regardless of bandwidth.

✨ Features

• Grain: Implemented resolution-dependent grain scaling. Grain blur radius and noise amplitude now scale automatically with image resolution (reference 2K), ensuring consistent visual graininess across different image sizes.