Fixes to make part 4.1 work

Author: JanFSchulte

environment.yml

@@ -20,3 +20,4 @@ dependencies:
       - conifer==1.5
       - pysr==0.16.3
       - xgboost==1.7.5
+      - zstd

part4.1_HG_quantization.ipynb

@@ -307,7 +307,7 @@
     "import hls4ml\n",
     "import plotting\n",
     "\n",
-    "hls_model = hls4ml.converters.convert_from_keras_model(proxy, output_dir='model_3.1/hls4ml_prj', part='xcu250-figd2104-2L-e')\n",
+    "hls_model = hls4ml.converters.convert_from_keras_model(proxy, output_dir='model_3.1/hls4ml_prj', part='xcu250-figd2104-2L-e', backend='Vitis')\n",
     "hls_model.compile()\n",
     "\n",
     "X_test = np.ascontiguousarray(X_test)\n",