feat(nix): fetch model files

nix/shells/default/default.nix

@@ -1,12 +1,20 @@
 { pkgs, lib, ... }:
 let
-    # Libs are needed to run the examples
+    # Libs and model files are needed to run the examples for testing purposes
     voskVersion = "0.3.45";
     arch = builtins.elemAt (lib.strings.splitString "-" pkgs.system) 0;
     voskLib = pkgs.fetchzip {
         url = "https://github.com/alphacep/vosk-api/releases/download/v${voskVersion}/vosk-linux-${arch}-${voskVersion}.zip";
         hash = "sha256-ToMDbD5ooFMHU0nNlfpLynF29kkfMknBluKO5PipLFY=";
     };
+    model = pkgs.fetchzip {
+        url = "https://alphacephei.com/vosk/models/vosk-model-small-en-us-0.15.zip";
+        hash = "sha256-CIoPZ/krX+UW2w7c84W3oc1n4zc9BBS/fc8rVYUthuY=";
+    };
+    speakerModel = pkgs.fetchzip {
+        url = "https://alphacephei.com/vosk/models/vosk-model-spk-0.4.zip";
+        hash = "sha256-wpTfZnEL1sCfpLhp+l62d8GcOinR15XnSHaLVASH4RA=";
+    };
 in
 pkgs.mkShell {
     buildInputs = with pkgs; [
@@ -22,4 +30,8 @@ pkgs.mkShell {
         pkgs.stdenv.cc.cc
         voskLib
     ];
+
+    # Run the examples like "cargo run --example <example> $MODEL $SPEAKER_MODEL" etc.
+    MODEL = model;
+    SPEAKER_MODEL = speakerModel;
 }