Add tool cache system to be used by tool methods called by agents

[wli51]

Motivation

If agent experiment 1 queried the chembl API of drugs A, B, C. It is highly likely that over repeated experiments subsequent agents will also query the same information of the same drugs.
Having these decorators that will automatically cache (persistently) these tool call - return will speed up future agent runs and to some extent alleviate the rate limiting problem.

Introduces:

1. tools/tool_cache/cache_config.py: allows programmatic setting of cache location on disk, capacity etc.
2. tools/tool_cache/cache_manager.py: simple module that wraps the python diskcache to access cache and info
3. tools/tool_cache/cache_decorator.py: module containing the actual decorator for caching, the cache hit/miss logic are here
4. tests for the above modules

Updates

1. ROADMAP.md: reflect the addition of functionality

Once this PR and #6 gets merged a PR implementing the chembl tool will follow.