langchain-anthropic: `cache_control` on a `tool_use` content block is silently dropped when a matching `tool_calls` item exists

### Submission checklist - [x] This is a bug, not a usage question. - [x] I added a clear and descriptive title that summarizes this issue. - [x] I used the GitHub search to find a similar question and didn't find it. - [x] I am sure that this is a bug in LangChain rather than my code. - [x] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package). - [x] This is not related to the langchain-community package. - [x] I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS. ### Package (Required) - [ ] langchain - [ ] langchain-openai - [x] langchain-anthropic - [ ] langchain-classic - [ ] langchain-core - [ ] langchain-model-profiles - [ ] langchain-tests - [ ] langchain-text-splitters - [ ] langchain-chroma - [ ] langchain-deepseek - [ ] langchain-exa - [ ] langchain-fireworks - [ ] langchain-groq - [ ] langchain-huggingface - [ ] langchain-mistralai - [ ] langchain-nomic - [ ] langchain-ollama - [ ] langchain-openrouter - [ ] langchain-perplexity - [ ] langchain-qdrant - [ ] langchain-xai - [ ] Other / not sure / general ### Related Issues / PRs _No response_ ### Reproduction Steps / Example Code (Python) ```python from langchain_core.messages import AIMessage, HumanMessage, ToolCall from langchain_anthropic.chat_models import _format_messages ai = AIMessage( content=[ {"type": "text", "text": "Let me check."}, { "type": "tool_use", "id": "toolu_1", "name": "get_weather", "input": {"city": "Paris"}, "cache_control": {"type": "ephemeral"}, # breakpoint on the tool_use block }, ], tool_calls=[ToolCall(name="get_weather", args={"city": "Paris"}, id="toolu_1")], ) _, formatted = _format_messages([HumanMessage(content="weather?"), ai]) out = formatted[-1]["content"] print(out) # cache_control is gone # [{'type': 'text', 'text': 'Let me check.'}, {'type': 'tool_use', 'name':…