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/two_agent_debate_tools.ipynb

@@ -22,17 +22,13 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "from typing import List, Dict, Callable\n",
-    "from langchain.chains import ConversationChain\n",
+    "from typing import List, Callable\n",
     "from langchain.chat_models import ChatOpenAI\n",
-    "from langchain.llms import OpenAI\n",
     "from langchain.memory import ConversationBufferMemory\n",
-    "from langchain.prompts.prompt import PromptTemplate\n",
     "from langchain.schema import (\n",
     "    AIMessage,\n",
     "    HumanMessage,\n",
     "    SystemMessage,\n",
-    "    BaseMessage,\n",
     ")"
    ]
   },
@@ -49,7 +45,6 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "from langchain.agents import Tool\n",
     "from langchain.agents import initialize_agent\n",
     "from langchain.agents import AgentType\n",
     "from langchain.agents import load_tools"