Feat/prompts caching

[amri369]

Summary

Integrate prompts list caching in MCP Servers. This allows agents to fetch prompts from local memory when cache_prompts_list is set to True. Otherwise, every time an agent runs, it calls list_prompts() on the MCP Server.

Key changes:

• Updated the implementation of list_prompts in _MCPServerWithClientSession to integrate caching using the same design pattern as caching integration in list_tools.
• Created example that uses caching with working demonstration.
• Updated documentation with caching setting.
• Renamed test test_server_caching_works to test_server_caching_prompts_works in tests/mcp/test_caching.py.

Note: This PR does not implement caching in get_prompt which can be useful in certain situations.

Test plan

Unit tests: Added 1 unit test in tests/mcp/test_caching.py to cover prompts list caching.

Example verification: Created working example with MCP server and client.
All tests pass: 523/523 tests passing after adding optional dependencies

Checks

[x] I've added new tests (if relevant)
[x] I've added/updated the relevant documentation
[x] I've run make lint and make format
[x] I've made sure tests pass