decouple sacp core from rmcp

[codefromthecrypt]

Right now, goose doesn't use the mcp_server package in the sacp crate, yet has to pull the dependency transitively.

sacp shouldn't have a strict dependency on rmcp and at a glance, it seems sacp-rmcp intends to decouple. I'd love to have this decoupling complete, and remove a distraction of multiple rmcp versions in goose triggered by code we don't use.

I think there are two main ways out:

1. Move the rmcp code to sacp-rmcp, so that sacp is no longer pulling the dep or even needing to compile it

• There's likely a reason this wasn't done before.. if not, best way out IMHO.

2. Make rmcp optional in sacp but keep the code where it is

• In src/sacp/Cargo.toml:
  • rmcp = { workspace = true, optional = true, features = ["server"] }
  • [features] mcp-server = ["rmcp"]
• In src/sacp/src/lib.rs and any features that depend on McpServer #[cfg(feature = "mcp-server")] pub mod mcp_server
• Update crates that actually use this, such as sacp-rmcp, to depend on sacp with features = ["mcp-server"]

3. your answer here!