Fix: defined default var for langchain cache path to enable custom path (issue 987)

[necjamahim]

When defining lc_cache_path and enabling cache in config:

# Enable third parties caching (e.g LangChain cache)
cache = true
lc_cache_path = './.custom-cache-path.db'

TypeError is thrown:

TypeError: chainlit.config.ProjectSettings() got multiple values for keyword argument 'lc_cache_path'

[tpatel]

Thanks for your code, I've added two comments.

[tpatel]

I believe you're missing something to change the project_config["lc_cache_path"] value, like:

Suggested change

	project_settings = ProjectSettings(
	project_config["lc_cache_path"] = project_config.get("lc_cache_path", lc_cache_path)
	project_settings = ProjectSettings(

[necjamahim]

the way i understand it and tested it locally, possible custom path will be picked up by toml_dict module here:

project_config = toml_dict.get("project", {})

or will default to default value as proposed by my PR here

# default to "{config_dir}/.langchain.db"
lc_cache_path: Optional[str] = os.path.join(config_dir, ".langchain.db")

[tpatel]

I'm not sure to understand why you've removed this?

[necjamahim]

it is because previous line st_llm_cache generates sqlite db file at path

set_llm_cache(SQLiteCache(database_path=config.project.lc_cache_path))

consequently in next line we want to inform cache was generated by testing if path exists and not the opposite. I hope I was clear - was trying not to use too many "if", "not" in the explaination