## Summary
This PR standardizes all text file I/O to use `UTF-8`. This eliminates
OS-specific defaults (e.g. Windows `cp1252`) and ensures consistent,
Unicode-safe behavior across platforms.
## Breaking changes
Users on systems with a default encoding which is not utf-8 may see
decoding errors from the following code paths:
* langchain_core.vectorstores.in_memroy.InMemoryVectorStore.load
* langchain_core.prompts.loading.load_prompt
* `from_template` in AIMessagePromptTemplate,
HumanMessagePromptTemplate, SystemMessagePromptTemplate
## Migration
Change the encoding of files that are encoded with a non utf-8 encoding to utf-8.
This auto generates partner migrations.
At the moment the migration is from community -> partner.
So one would need to run the migration script twice to go from langchain to partner.
Add script to help generate migrations.
This works well for partner packages. Migrations are generated based on run time rather than static analysis (much simpler to get the correct migrations implemented).
The script for generating migrations from langchain to community still needs work.
