feat: support MCP resources

- [x] I have looked for existing issues (including closed) about this

## Feature Request

ref: https://github.com/0xPlaygrounds/rig/discussions/1036

Going to be honest, I am not really sure how we would add this in. We would probably need another kind of MCP resource state that the Agent holds and then at provider message creation time we'd fetch the resources.

### Motivation

Better support for MCP Resources

### Proposal

TBD

The issue references a discussion #1036 about MCP (Model Context Protocol) resources. Start by reading that discussion to understand the context. The proposal mentions needing a new MCP resource state in the Agent and fetching resources at provider message creation. Look at the existing MCP and Agent code to see how resources are currently handled. 'Done' would be a design and implementation that integrates MCP resources into the system.

Scritto dal modello di indicizzazione a partire dal testo della issue.