agent: Handle attempts to use hallucinated tools (#29946)

This change:

1. Catches attempts to use missing tools. If this happens, we now send
Agent a message listing available tools, after which Agent can
gracefully recover. Prior behavior: thread would stop in a broken state.

Example of a hallucinated call and a message we send back: 

![image](https://github.com/user-attachments/assets/92a8f700-b192-4038-8c7e-0a74ca2e0146)

2. Adds evals for hallucinated tool use and imagined edits
3. Adds ability to configure a profile name in evals.



Release Notes:

- N/A

Cargo.lock

@@ -5019,6 +5019,7 @@ version = "0.1.0"
 dependencies = [
  "agent",
  "anyhow",
+ "assistant_settings",
  "assistant_tool",
  "assistant_tools",
  "async-trait",