Bumps `langchain-core` to `1.4.7` for the next patch release and updates
downstream minimum `langchain-core` requirements so package locks
resolve against the new core version.
This also refreshes the runnable snapshots that embed `lc_versions`
metadata so the version consistency check continues to validate
checked-in artifacts.
Validated with `python libs/core/scripts/check_version.py`, `uv lock
--check` across package lockfiles, and the core runnable tests that own
the updated snapshots with local LangSmith tracing env disabled.
it looks scary but i promise it is not
improving documentation consistency across core. primarily update
docstrings and comments for better formatting, readability, and
accuracy, as well as add minor clarifications and formatting
improvements to user-facing documentation.
