rubberband: update to 1.9.1

Changes in Rubber Band v1.9.1

* Switch build system from Makefiles and Visual Studio project to
  Meson/Ninja for all platforms. There are still Makefiles and VS
  projects included in otherbuilds/ for those who wish to use them to
  build the static library directly
* Make various fixes to improve sound quality when pitch-shifting
  dynamically in real-time (requires libsamplerate)
* Fix floating-point exception when a very very long stretch factor
  is presented
* Move the two directories that together provide the .NET interface
  (rubberband-sharp and rubberband-dll) into their own subdir (dotnet)
* Ensure the library builds and runs correctly on ARM Mac (Apple
  Silicon, M1), and also on Windows using the Visual C++ Clang
  front-end

The API is unchanged and the library is binary compatible with
version 1.7.

(nia)