refactor: Remove unused constants and functions from sequencer utilities and envelopes

Commit notes

This commit cleans up the codebase by removing unused constants, such as NUM_BARS and TRACK_COLORS, as well as the applyADSREnvelope function from the envelopes module. Additionally, it streamlines the sequencer utilities by eliminating redundant functions and optimizing the structure of step creation. These changes enhance maintainability and reduce clutter in the codebase.