[rust-guard] Deduplicate owner/repo parsing paths in labels backend (#5548)

## ✨ Enhancement

This change removes two duplication hotspots in
`guards/github-guard/rust-guard/src/labels/backend.rs` without altering
behavior: repeated item-scan logic in owner-type extraction and repeated
`full_name`/`fullName` lookup logic in repo ID extraction. The result is
a smaller, more maintainable parsing path with unchanged field
precedence and fallback behavior.

**What does this improve?**
- **Owner-type lookup deduplication**
- Introduces `find_org_in_items(items, repo_id)` and reuses it for both
response shapes:
    - `{ "items": [...] }`
    - plain array `[...]`
- **Repo ID field lookup deduplication**
- Replaces duplicate `if` blocks for `"full_name"` and `"fullName"` with
a single ordered loop.
- **Regression coverage for refactor paths**
  - Adds focused tests for:
    - plain-array owner/org extraction path
    - camelCase `fullName` repo ID extraction path

**Why is this valuable?**
- Reduces copy/paste control flow in high-traffic parsing helpers.
- Centralizes repo-ID match logic used by owner-type extraction.
- Makes future alias additions and edge-case coverage lower-risk.

**Implementation approach:**
- Extracted shared iterator-based helper:

```rust
fn find_org_in_items(items: &[Value], repo_id: &str) -> Option<bool> {
    items.iter().find_map(|item| {
        let item_repo_id = repo_id_from_repo_object(item)?;
        if item_repo_id.eq_ignore_ascii_case(repo_id) {
            owner_type_from_repo_object(item)
        } else {
            None
        }
    })
}
```

- Updated `owner_is_org_from_items` to delegate both array shapes to the
helper.
- Updated `repo_id_from_repo_object` to iterate `["full_name",
"fullName"]` in priority order, preserving existing behavior.

Author: lpcox

guards/github-guard/rust-guard/src/labels/backend.rs

@@ -1243,6 +1243,47 @@ mod tests {
         });
         assert_eq!(extract_owner_is_org(&response, "myorg/myrepo"), None);
     }
+
+    #[test]
+    fn test_extract_owner_is_org_plain_array_response() {
+        let response = serde_json::json!([{
+            "full_name": "myorg/myrepo",
+            "private": false,
+            "owner": { "login": "myorg", "type": "Organization" }
+        }]);
+        assert_eq!(extract_owner_is_org(&response, "myorg/myrepo"), Some(true));
+    }
+
+    #[test]
+    fn test_extract_owner_is_org_first_match_missing_type_returns_none() {
+        let response = serde_json::json!({
+            "items": [
+                {
+                    "full_name": "myorg/myrepo",
+                    "private": false,
+                    "owner": { "login": "myorg" }
+                },
+                {
+                    "full_name": "myorg/myrepo",
+                    "private": false,
+                    "owner": { "login": "myorg", "type": "Organization" }
+                }
+            ]
+        });
+        assert_eq!(extract_owner_is_org(&response, "myorg/myrepo"), None);
+    }
+
+    #[test]
+    fn test_repo_id_from_repo_object_full_name_camelcase() {
+        let item = serde_json::json!({
+            "fullName": "myorg/myrepo",
+            "owner": { "login": "myorg", "type": "Organization" }
+        });
+        assert_eq!(
+            repo_id_from_repo_object(&item),
+            Some("myorg/myrepo".to_string())
+        );
+    }
 }
 
 fn repo_visibility_from_items(value: &Value, repo_id: &str) -> Option<bool> {
@@ -1384,7 +1425,7 @@ fn owner_type_from_repo_object(item: &Value) -> Option<bool> {
 }
 
 fn repo_id_from_repo_object(item: &Value) -> Option<String> {
-    for field in &["full_name", "fullName"] {
+    for field in ["full_name", "fullName"] {
         if let Some(full_name) = item.get(field).and_then(|v| v.as_str()) {
             if !full_name.is_empty() {
                 return Some(full_name.to_string());