fix: increase default stdio connection timeout from 30s to 60s

Some MCP servers (especially those with heavy initialization like
npm install or large model loading) can take longer than 30s to
complete the handshake. Increase the default to 60s to reduce
spurious connection timeout failures.

Signed-off-by: Mohammod Al Amin Ashik <maa.ashik00@gmail.com>

Author: its-mash

crates/mcpmux-gateway/src/pool/connection.rs

@@ -24,7 +24,7 @@ use super::transport::{
 };
 
 /// Default connection timeout
-const DEFAULT_CONNECT_TIMEOUT: Duration = Duration::from_secs(30);
+const DEFAULT_CONNECT_TIMEOUT: Duration = Duration::from_secs(60);
 
 /// Result of a connection attempt
 #[derive(Debug)]