[no ci] notebook tests: increase timeout, fix platform/backend dependent code

Torch is very slow, so I had to increase the timeout accordingly.

Author: vpratz

examples/From_ABC_to_BayesFlow.ipynb

@@ -38,7 +38,10 @@
    "outputs": [],
    "source": [
     "import numpy as np\n",
-    "import matplotlib.pyplot as plt"
+    "import matplotlib.pyplot as plt\n",
+    "import tempfile\n",
+    "from pathlib import Path\n",
+    "import platform"
    ]
   },
   {
@@ -322,7 +325,9 @@
     ")\n",
     "\n",
     "# generate a temporary SQLite DB\n",
-    "abc_id = abc.new(\"sqlite:////tmp/mjp.db\", observations)"
+    "prefix = \"sqlite:///\" if platform.system() == \"Windows\" else \"sqlite:////\"\n",
+    "db_path = (Path(tempfile.gettempdir()).absolute() / \"mjp.db\").as_uri().replace(\"file:///\", prefix)\n",
+    "abc_id = abc.new(db_path, observations)"
    ]
   },
   {

examples/SIR_Posterior_Estimation.ipynb

@@ -19,7 +19,11 @@
    "source": [
     "import os\n",
     "# Set to your favorite backend\n",
-    "os.environ[\"KERAS_BACKEND\"] = \"jax\""
+    "if \"KERAS_BACKEND\" not in os.environ:\n",
+    "    # set this to \"torch\", \"tensorflow\", or \"jax\"\n",
+    "    os.environ[\"KERAS_BACKEND\"] = \"tensorflow\"\n",
+    "else:\n",
+    "    print(f\"Using '{os.environ['KERAS_BACKEND']}' backend\")"
    ]
   },
   {

examples/Two_Moons_Starter.ipynb

@@ -24,7 +24,11 @@
    "source": [
     "import os\n",
     "# Set to your favorite backend\n",
-    "os.environ[\"KERAS_BACKEND\"] = \"jax\""
+    "if \"KERAS_BACKEND\" not in os.environ:\n",
+    "    # set this to \"torch\", \"tensorflow\", or \"jax\"\n",
+    "    os.environ[\"KERAS_BACKEND\"] = \"tensorflow\"\n",
+    "else:\n",
+    "    print(f\"Using '{os.environ['KERAS_BACKEND']}' backend\")"
    ]
   },
   {

tests/utils/jupyter.py

@@ -10,10 +10,10 @@ def run_notebook(path):
     checkpoint_path = path.parent / "checkpoints"
     # only clean up if the directory did not exist before the test
     cleanup_checkpoints = not checkpoint_path.exists()
-    with open(str(path)) as f:
+    with open(str(path), encoding="utf-8") as f:
         nb = nbformat.read(f, nbformat.NO_CONVERT)
 
-    kernel = ExecutePreprocessor(timeout=600, kernel_name="python3", resources={"metadata": {"path": path.parent}})
+    kernel = ExecutePreprocessor(timeout=3600, kernel_name="python3", resources={"metadata": {"path": path.parent}})
 
     try:
         result = kernel.preprocess(nb)