v4.0.0

Added

• no_std support
  std math replaced with libm.

Modified

• Memory-efficient API
  FloatOverlay and Overlay use a reusable buffer to reduce allocation overhead, improving performance by 5–15% in repeated operations.
  OverlayGraph is now a reference view (no longer owns geometry data)

• Optional multithreading
  allow_multithreading is now an optional feature and disabled by default.