feat(radio): allow setting DI_FM_KEY as env variable

packages/mpv-tuner.nix

@@ -0,0 +1,22 @@
+{
+  writeText,
+  lib,
+  writers,
+  mpv,
+  gnused,
+  di-fm-key-file,
+  findutils,
+}: let
+  streams = import ../lib/streams.nix {
+    di-fm-key = "%DI_FM_KEY%";
+  };
+  streams-list = writeText "streams.txt" (lib.concatMapStringsSep "\n" (station: station.stream) streams);
+in
+  writers.writeDashBin "mpv-tuner" ''
+    if [ -z ''${DI_FM_KEY} ]; then
+      DI_FM_KEY=$(cat "${di-fm-key-file}")
+    fi
+    shuf ${streams-list} \
+      | ${gnused}/bin/sed s/%DI_FM_KEY%/"$DI_FM_KEY"/ \
+      | ${findutils}/bin/xargs ${mpv}/bin/mpv
+  ''