zeta2: Support qwen3-minimal prompt format (#42902)

This prompt is for a fine-tuned model. It has the following changes,
compared to `minimal`:
- No instructions at all, except for one sentence at the beginning of
the prompt.
- Output is a simplified unified diff -- hunk headers have no line
counts (e.g., `@@ -20 +20 @@`)
- Qwen's FIM tokens are used where possible (`<|file_sep|>`,
`<|fim_prefix|>`, `<|fim_suffix|>`, etc.)

To evaluate this model:
```
ZED_ZETA2_MODEL=zeta2-exp [usual zeta-cli eval params ...]  --prompt-format minimal-qwen
```

This will point to the most recent Baseten deployment of zeta2-exp
(which may change in the future, so the prompt-format may get out of
sync).

Release Notes:

- N/A

crates/zeta_cli/src/main.rs

@@ -176,6 +176,7 @@ enum PromptFormat {
     NumberedLines,
     OldTextNewText,
     Minimal,
+    MinimalQwen,
 }
 
 impl Into<predict_edits_v3::PromptFormat> for PromptFormat {
@@ -187,6 +188,7 @@ impl Into<predict_edits_v3::PromptFormat> for PromptFormat {
             Self::NumberedLines => predict_edits_v3::PromptFormat::NumLinesUniDiff,
             Self::OldTextNewText => predict_edits_v3::PromptFormat::OldTextNewText,
             Self::Minimal => predict_edits_v3::PromptFormat::Minimal,
+            Self::MinimalQwen => predict_edits_v3::PromptFormat::MinimalQwen,
         }
     }
 }