chore: move types out of config.rs into config_types.rs (#1054)

`config.rs` is already quite long without these definitions. Since they
have no real dependencies of their own, let's move them to their own
file so `config.rs` can focus on the business logic of loading a config.

codex-rs/core/src/mcp_connection_manager.rs

@@ -19,7 +19,7 @@ use mcp_types::Tool;
 use tokio::task::JoinSet;
 use tracing::info;
 
-use crate::mcp_server_config::McpServerConfig;
+use crate::config_types::McpServerConfig;
 
 /// Delimiter used to separate the server name from the tool name in a fully
 /// qualified tool name.