legacy serialization mapping points to outdated module namespace

### 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 - [ ] 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 #36229 ### Reproduction Steps / Example Code (Python) ```python from langchain_core.load.mapping import SERIALIZABLE_MAPPING key = ("langchain", "schema", "runnable", "HubRunnable") print("HubRunnable target:", SERIALIZABLE_MAPPING[key]) ``` ### Error Message and Stack Trace (if applicable) ```shell No direct runtime stack trace is required to reproduce this issue. ``` ### Description I found that some legacy serialization mappings in langchain_core.load.mapping resolve to outdated module namespaces after package reorganization. Expected behavior is that specific legacy IDs should resolve to langchain_classic. ### System Info System Information ------------------ > OS: Windows > OS Version: 10.0.19045 > Python Version: 3.13.2 (tags/v3.13.2:4f8bb39, Feb 4 2025, 15:23:48) [MSC v.1942 64 bit (AMD64)] Package Informatio…