`convert_to_openai_image_block` drops the `detail` field for image content blocks

### Checked other resources - [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 - [ ] langchain-anthropic - [ ] langchain-classic - [x] langchain-core - [ ] langchain-model-profiles - [x] 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 """Regression tests for detail field forwarding in OpenAI image block converters. Run: pytest -vvvl test_image_detail.py """ import pytest from langchain_core.messages.block_translators.openai import ( convert_to_openai_data_block, convert_to_openai_image_block, ) def _test_id(val: dict) -> str: """Generate readable test ID from input block.""" if "detail" in val: loc = "top_level" elif "extras" in val: loc = "extras" elif "metadata" in val: loc = "metadata" else: loc = "no_detail" if "source_type" in val: src = f"source_type_{val['source_type']}" elif "base64" in val: src = "base64" elif "url" in val: src = "url" else: src = "unknown" retur…