zeta2: Allow provider to suggest edits in different files (#39110)

Release Notes:

- N/A

---------

Co-authored-by: Agus Zubiaga <agus@zed.dev>

crates/cloud_llm_client/src/predict_edits_v3.rs

@@ -43,15 +43,24 @@ pub struct PredictEditsRequest {
     pub prompt_format: PromptFormat,
 }
 
-#[derive(Default, Debug, Clone, Copy, Serialize, Deserialize, PartialEq, EnumIter)]
+#[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq, EnumIter)]
 pub enum PromptFormat {
-    #[default]
     MarkedExcerpt,
     LabeledSections,
     /// Prompt format intended for use via zeta_cli
     OnlySnippets,
 }
 
+impl PromptFormat {
+    pub const DEFAULT: PromptFormat = PromptFormat::LabeledSections;
+}
+
+impl Default for PromptFormat {
+    fn default() -> Self {
+        Self::DEFAULT
+    }
+}
+
 impl PromptFormat {
     pub fn iter() -> impl Iterator<Item = Self> {
         <Self as strum::IntoEnumIterator>::iter()