Onset detection and save

[kunitoki]

This pull request introduces a new SuperFlux auto-slicing feature to the VelociLoops library, adds a fuzzing target, and improves build and documentation consistency. The most significant changes are the addition of the SuperFlux onset detection API and demo, expanded documentation, and improved build options for coverage, sanitizers, and parallelization.

New SuperFlux auto-slicing feature:

• Added VLSuperFluxOptions struct and related API functions (vl_superflux_default_options, vl_create_from_superflux) to support SuperFlux onset detection for automatic loop slicing. This includes full documentation and examples in README.md, docs/api.md, and include/velociloops.h. [1] [2] [3] [4] [5] [6]

Build system and CI improvements:

• Standardized CMake options for coverage, sanitizers, and fuzzing to use VELOCILOOPS_ENABLE_* variables, updated all related workflow files, and improved parallelization in builds and tests. [1] [2] [3] [4] [5] [6]

Fuzzing support:

• Added a new fuzzing target with fuzz/CMakeLists.txt and proper CMake integration for building with fuzzing and sanitizers enabled. [1] [2]

Documentation and code style:

• Expanded API documentation for new features, clarified usage, and improved code examples for readability and modern C style. [1] [2] [3] [4] [5] [6] [7] [8]

API cleanup:

• Removed the unimplemented vl_set_output_sample_rate function from both the header and documentation. [1] [2]