## 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.
083fbfb0d1