mpich: deprecate stringly-typed withPm

  replaces the need for the `extraPackages` option, this option will be

  deprecated in future releases.

- The `mpich` package expression now requires `withPm` to be a list, e.g. `"hydra:gforker"` becomes `[ "hydra" "gforker" ]`.

- QtMultimedia has changed its default backend to `QT_MEDIA_BACKEND=ffmpeg` (previously `gstreamer` on Linux or `darwin` on MacOS).

  The previous native backends remain available but are now minimally maintained. Refer to [upstream documentation](https://doc.qt.io/qt-6/qtmultimedia-index.html#ffmpeg-as-the-default-backend) for further details about each platform.

} :

let

  processManagers = if builtins.isList withPm then

    withPm

  else

    builtins.filter builtins.isString (builtins.split ":" withPm);

  withPm' = if processManagers != [ ] then builtins.concatStringsSep ":" processManagers else "no";

  withPmStr = if withPm != [ ] then builtins.concatStringsSep ":" withPm else "no";

in

assert (ch4backend.pname == "ucx" || ch4backend.pname == "libfabric");

  configureFlags = [

    "--enable-shared"

    "--with-pm=${withPm'}"

    "--with-pm=${withPmStr}"

  ] ++ lib.optionals (lib.versionAtLeast gfortran.version "10") [

    "FFLAGS=-fallow-argument-mismatch" # https://github.com/pmodels/mpich/issues/4300

    "FCFLAGS=-fallow-argument-mismatch"

  meta = with lib; {

    # As far as we know, --with-pmix silently disables all of `--with-pm`

    broken = pmixSupport && processManagers != [ ];

    broken = pmixSupport && withPm != [ ];

    description = "Implementation of the Message Passing Interface (MPI) standard";