feat: basic pr diff rendering

fixtures/github/issues.pull_request_file_tree.PR_kwDONovem85.json

@@ -0,0 +1,19 @@
+{
+  "node": {
+    "__typename": "PullRequest",
+    "files": {
+      "edges": [
+        {
+          "cursor": "file:PR_kwDONovem85:1",
+          "node": {
+            "changeType": "MODIFIED",
+            "additions": 42,
+            "deletions": 7,
+            "path": "src/api/repo.rs",
+            "viewerViewedState": "UNVIEWED"
+          }
+        }
+      ]
+    }
+  }
+}