[Feature Request] Graph RAG support caching and parallelism

### Required prerequisites

- [X] I have searched the [Issue Tracker](https://github.com/camel-ai/camel/issues) and [Discussions](https://github.com/camel-ai/camel/discussions) that this hasn't already been reported. (+1 or comment there if it has.)
- [ ] Consider asking first in a [Discussion](https://github.com/camel-ai/camel/discussions/new).

### Motivation

Inspired by communication with community members, we can enhance Graph RAG by adding support for caching and parallelism

### Solution

_No response_

### Alternatives

_No response_

### Additional context

_No response_

The issue identifies Graph RAG as the area for change but names no files, entry points, tests, or requirements. Start by locating the Graph RAG implementation and determine the intended caching and parallelism behavior. The work is done when those requirements are defined, implemented, and covered by appropriate tests.

Written by the indexing model from the issue text.