Lint Python notebooks with ruff. (#12677)

The new ruff version fixed the blocking bugs, and I was able to fairly
easily us to a passing state: ruff fixed some issues on its own, I fixed
a handful by hand, and I added a list of narrowly-targeted exclusions
for files that are currently failing ruff rules that we probably should
look into eventually.

I went pretty lenient on the docs / cookbooks rules, allowing dead code
and such things. Perhaps in the future we may want to tighten the rules
further, but this is already a good set of checks that found real issues
and will prevent them going forward.

cookbook/forward_looking_retrieval_augmented_generation.ipynb

@@ -56,7 +56,8 @@
    "source": [
     "import os\n",
     "\n",
-    "os.environ[\"SERPER_API_KEY\"] = \"\"os.environ[\"OPENAI_API_KEY\"] = \"\""
+    "os.environ[\"SERPER_API_KEY\"] = \"\"\n",
+    "os.environ[\"OPENAI_API_KEY\"] = \"\""
    ]
   },
   {
@@ -66,17 +67,12 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "import re\n",
-    "\n",
-    "import numpy as np\n",
-    "\n",
     "from langchain.schema import BaseRetriever\n",
     "from langchain.callbacks.manager import (\n",
     "    AsyncCallbackManagerForRetrieverRun,\n",
     "    CallbackManagerForRetrieverRun,\n",
     ")\n",
     "from langchain.utilities import GoogleSerperAPIWrapper\n",
-    "from langchain.embeddings import OpenAIEmbeddings\n",
     "from langchain.chat_models import ChatOpenAI\n",
     "from langchain.llms import OpenAI\n",
     "from langchain.schema import Document\n",