overlays: split the pipewire ffado tweak into a `preferences` overlay

flake.nix

@@ -174,6 +174,7 @@
         disable-flakey-tests = final: prev: import ./overlays/disable-flakey-tests.nix final prev;
         pkgs = final: prev: import ./overlays/pkgs.nix final prev;
         pins = final: prev: import ./overlays/pins.nix final prev;
+        preferences = final: prev: import ./overlays/preferences.nix final prev;
         optimizations = final: prev: import ./overlays/optimizations.nix final prev;
         passthru = final: prev:
           let

overlays/all.nix

@@ -5,6 +5,7 @@
 final: prev:
 let
   pkgs = import ./pkgs.nix;
+  preferences = import ./preferences.nix;
   disable-flakey-tests = import ./disable-flakey-tests.nix;
   optimizations = import ./optimizations.nix;
   cross = import ./cross.nix;
@@ -18,6 +19,7 @@ let
 in
   renderOverlays [
     pkgs
+    preferences
     disable-flakey-tests
     (ifCross optimizations)
     (ifCross cross)

overlays/disable-flakey-tests.nix

@@ -50,12 +50,6 @@ in {
     mesonFlags = [ "-Dtests=disabled" ];
   }) prev.libwacom;
 
-  pipewire = prev.pipewire.override {
-    # avoid a dep on python3.10-PyQt5, which has mixed qt5 versions.
-    # this means we lose firewire support (oh well..?)
-    ffadoSupport = false;
-  };
-
   pythonPackagesExtensions = prev.pythonPackagesExtensions ++ [
     (py-next: py-prev: {
       pyarrow = py-prev.pyarrow.overridePythonAttrs (upstream: {

overlays/preferences.nix

@@ -0,0 +1,10 @@
+# personal preferences
+# prefer to encode these in `sane.programs`
+# resort to this method for e.g. system dependencies, or things which are referenced from too many places.
+(next: prev: {
+  pipewire = prev.pipewire.override {
+    # avoid a dep on python3.10-PyQt5, which has mixed qt5 versions.
+    # this means we lose firewire support (oh well..?)
+    ffadoSupport = false;
+  };
+})