Skip attribution for direct MCP tool calls (#58938)

## Why

`CodexThread::call_mcp_tool` returns only the tool result, so computing attribution and creating a cached runtime binding for these calls is unnecessary.

## What changed

Add `McpRuntime::latest_call_tool_without_attribution` and use it for direct thread calls. Validate the call, wait for server startup, and dispatch through the latest connections without capturing an attribution binding.

## Testing

Extend the runtime binding cache test to verify that a successful call without attribution leaves the cached binding empty. Update the test server to return a successful tool result.

GitOrigin-RevId: 898e655d9a0174ddaf71c390757d6fc9a5a61780

codex-rs/core/src/codex_thread.rs

@@ -1369,12 +1369,8 @@ impl CodexThread {
         self.session
             .services
             .mcp_runtime
-            .latest_call_tool(
-                server, tool, /*environment_id*/ None, arguments, meta,
-                /*requested_timeout*/ None, /*wait_for_server*/ true,
-            )
+            .latest_call_tool_without_attribution(server, tool, arguments, meta)
             .await
-            .map(|call| call.result)
     }
 
     pub fn enabled(&self, feature: Feature) -> bool {