cloud_llm_client: Add derives for edit prediction fields (#51968)

## Context

This PR adds some derives which make tracing easier on cloud side.

## Self-Review Checklist

<!-- Check before requesting review: -->
- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- N/A

crates/cloud_llm_client/src/cloud_llm_client.rs

@@ -111,7 +111,8 @@ pub struct PredictEditsBody {
     pub trigger: PredictEditsRequestTrigger,
 }
 
-#[derive(Default, Debug, Clone, Copy, Serialize, Deserialize)]
+#[derive(Default, Debug, Clone, Copy, Serialize, Deserialize, strum::AsRefStr)]
+#[strum(serialize_all = "snake_case")]
 pub enum PredictEditsRequestTrigger {
     Testing,
     Diagnostics,
@@ -170,7 +171,10 @@ pub struct EditPredictionRejection {
     pub e2e_latency_ms: Option<u128>,
 }
 
-#[derive(Default, Debug, Clone, Copy, Serialize, Deserialize, PartialEq)]
+#[derive(
+    Default, Debug, Clone, Copy, Serialize, Deserialize, PartialEq, Eq, Hash, strum::AsRefStr,
+)]
+#[strum(serialize_all = "snake_case")]
 pub enum EditPredictionRejectReason {
     /// New requests were triggered before this one completed
     Canceled,