Add a langchain_community.caches.DiskCache using diskcache

[rjurney]

Checked

• I searched existing ideas and did not find a similar one
• I added a very descriptive title
• I've clearly described the feature request and motivation for it

Feature request

There is no langchain_community.caches.DiskCache and I think there is a need for a simple LLM cache that persists across runs and doesn't require the use of a database. I think most LLM caching for ad hoc applications will use this if it exists.

Motivation

I need my cache to persist across runs for long running data augmentation pipelines.

Proposal (If applicable)

I am going to contribute an implementation I wrote for a langchain_commuity.caches.DiskCache cache that is similar to langchain_community.cache.InMemoryCache but uses an instance of diskcache.Cache in place of a Dict. The implementation isn't difficult and I think a lot of people will use this, particularly for long batch workflows such as my use case: data augmentation using an LLM.