Add Roots support to the MCP client and server

[gspencergoog]

Description

This adds roots support to the MCP client and server. It supports setting client roots when creating the client, but not modifying the roots once the client plugin is created. That will have to come later: changing the roots means that the available tools/prompts/resources might also change, and I didn't want to build dynamically changing tools because I wasn't clear on exactly how that was done. I did add support for the server to request the roots from the client (because some do that even if the roots don't change), which means that the client now registers handlers too.

Tests

• I also added some basic configuration unit tests for the client and server (Despite being verbose, they don't actually test that much, just the setup).

[gspencergoog]

@mbleigh Here is the roots support PR I said I'd send your way. Let me know if it's what you were expecting.

I've tested the client against a server that supports roots, and it seems to work as expected. It should probably have some integration tests too, so that the client (and server) would be tested against a fake server (and client).