VapourSynth API4 headers — vendored verbatim so the mvuscale native filter
builds without a VapourSynth SDK installed (self-contained CI).

Source: the `vapoursynth` distribution's `vapoursynth/include/` directory.
Copyright (c) 2012-2026 Fredrik Mellbin.

  VapourSynth4.h   LGPL-2.1-or-later
  VSConstants4.h   LGPL-2.1-or-later
  VSHelper4.h      WTFPL (Do What The Fuck You Want To Public License, v2)

Both licences are compatible with this project's GPL-3.0-or-later, and merely
#including these API headers to build a plugin is their intended use. They are
not modified. To refresh, copy them from a current `vapoursynth` install.
