chore: exclude p2p crate from workspace, slim tokio features

Move quicnprotochat-p2p to workspace.exclude so ~90 iroh-only
dependencies are not compiled in the default build. Narrow tokio
features from "full" to the subset actually used. The p2p crate
now pins its own dependency versions since it is outside the workspace.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

crates/quicnprotochat-p2p/Cargo.toml

@@ -7,6 +7,6 @@ license     = "MIT"
 
 [dependencies]
 iroh        = "0.96"
-tokio       = { workspace = true }
-tracing     = { workspace = true }
-anyhow      = { workspace = true }
+tokio       = { version = "1", features = ["macros", "rt-multi-thread", "time", "sync"] }
+tracing     = "0.1"
+anyhow      = "1"