feat: hot reload mcp servers (#8957)

### Summary
* Added `mcpServer/refresh` command to inform app servers and active
threads to refresh mcpServer on next turn event.
* Added `pending_mcp_server_refresh_config` to codex core so that if the
value is populated, we reinitialize the mcp server manager on the thread
level.
* The config is updated on `mcpServer/refresh` command which we iterate
through threads and provide with the latest config value after last
write.

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -156,6 +156,11 @@ client_request_definitions! {
         response: v2::McpServerOauthLoginResponse,
     },
 
+    McpServerRefresh => "config/mcpServer/reload" {
+        params: #[ts(type = "undefined")] #[serde(skip_serializing_if = "Option::is_none")] Option<()>,
+        response: v2::McpServerRefreshResponse,
+    },
+
     McpServerStatusList => "mcpServerStatus/list" {
         params: v2::ListMcpServerStatusParams,
         response: v2::ListMcpServerStatusResponse,