[MCP] Add support for resources (#5239)

This PR adds support for [MCP
resources](https://modelcontextprotocol.io/specification/2025-06-18/server/resources)
by adding three new tools for the model:
1. `list_resources`
2. `list_resource_templates`
3. `read_resource`

These 3 tools correspond to the [three primary MCP resource protocol
messages](https://modelcontextprotocol.io/specification/2025-06-18/server/resources#protocol-messages).

Example of listing and reading a GitHub resource tempalte
<img width="2984" height="804" alt="CleanShot 2025-10-15 at 17 31 10"
src="https://github.com/user-attachments/assets/89b7f215-2e2a-41c5-90dd-b932ac84a585"
/>

`/mcp` with Figma configured
<img width="2984" height="442" alt="CleanShot 2025-10-15 at 18 29 35"
src="https://github.com/user-attachments/assets/a7578080-2ed2-4c59-b9b4-d8461f90d8ee"
/>

Fixes #4956

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

@@ -223,10 +223,28 @@ async fn prompt_tools_are_consistent_across_requests() {
     // our internal implementation is responsible for keeping tools in sync
     // with the OpenAI schema, so we just verify the tool presence here
     let tools_by_model: HashMap<&'static str, Vec<&'static str>> = HashMap::from([
-        ("gpt-5", vec!["shell", "update_plan", "view_image"]),
+        (
+            "gpt-5",
+            vec![
+                "shell",
+                "list_mcp_resources",
+                "list_mcp_resource_templates",
+                "read_mcp_resource",
+                "update_plan",
+                "view_image",
+            ],
+        ),
         (
             "gpt-5-codex",
-            vec!["shell", "update_plan", "apply_patch", "view_image"],
+            vec![
+                "shell",
+                "list_mcp_resources",
+                "list_mcp_resource_templates",
+                "read_mcp_resource",
+                "update_plan",
+                "apply_patch",
+                "view_image",
+            ],
         ),
     ]);
     let expected_tools_names = tools_by_model