Add "View Image" tool (#2723)

Adds a "View Image" tool so Codex can find and see images by itself:

<img width="1772" height="420" alt="Screenshot 2025-08-26 at 10 40
04 AM"
src="https://github.com/user-attachments/assets/7a459c7b-0b86-4125-82d9-05fbb35ade03"
/>

codex-rs/core/tests/suite/prompt_caching.rs

@@ -191,7 +191,7 @@ async fn prompt_tools_are_consistent_across_requests() {
     let expected_instructions: &str = include_str!("../../prompt.md");
     // our internal implementation is responsible for keeping tools in sync
     // with the OpenAI schema, so we just verify the tool presence here
-    let expected_tools_names: &[&str] = &["shell", "update_plan", "apply_patch"];
+    let expected_tools_names: &[&str] = &["shell", "update_plan", "apply_patch", "view_image"];
     let body0 = requests[0].body_json::<serde_json::Value>().unwrap();
     assert_eq!(
         body0["instructions"],