refactor: Improve parameter handling in SequencerProcessor for better clarity and consistency

Commit notes

This commit refactors the SequencerProcessor class to enhance the handling of optional parameters across various audio effects. It replaces nullish coalescing with explicit checks for undefined values, improving code readability and ensuring consistent behavior. Additionally, it updates the logic for handling division values in step creation and copying, further streamlining the sequencer's functionality. These changes contribute to better maintainability and performance of the audio processing pipeline.