pyproject.toml is read with the locale encoding in unit tests — full inventory (4 call sites, one missed by #40588, one latent)

### 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) - [x] langchain - [ ] langchain-openai - [ ] langchain-anthropic - [x] 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-typesafe - [ ] langchain-xai - [ ] Other / not sure / general ### Related Issues / PRs Follow-up to #40588 (same defect class; complete inventory below). Merged precedent for Windows test portability: #39664. ### Reproduction Steps / Example Code (Python) ```python On Windows with a non-UTF-8 system locale (cp936), from a fresh clone: cd libs/langchain_v1 uv sync --group test PYTHONUTF8=0 uv run --group test pytest tests/unit_tests/test_version.py tests/unit_tests/test_dependencies.py \ "tests/unit_tests/agents/middleware/implementations/test_summarization.py::test_trigger_conditions_legacy_tuple_view_remove_in_2_0" -q (The same failure shows with a one-liner: PYTHONUTF8=0 python -c "open('libs/langchain_v1/pyproject.toml').read()") ``` ### Error Message and Stack Trace (if applicable) ```shell FAILED tests/unit_tests/test_version.py::test_version_matches_pyproject - Uni... FAILED…