test: raise the perf budget for opening a message to the conversation it now loads, and for the rows that fit on screen

Opening a message now fetches its conversation (Thread/get) and shows it in the reading pane, adds the address menus to each address, and shows a loading placeholder while a first message waits for its conversation. Shorter list rows put three more rows on screen, so searching and switching folders draw more rows, and the first-start notices sit above the list. Measured against a build of 5a020cf2f, the last green run, with component names kept. The open's extra pass that drew the mail view twice is fixed instead; the budget takes the rest. Render passes for opening go down from 8 to 6.

scripts/perf-guard/budget.json

@@ -1,22 +1,22 @@
 {
   "open": {
-    "commits": 8,
-    "renders": 475,
-    "requests": 1
+    "commits": 6,
+    "renders": 630,
+    "requests": 2
   },
   "search": {
     "commits": 9,
-    "renders": 454,
+    "renders": 513,
     "requests": 2
   },
   "folder (first visit)": {
-    "commits": 8,
-    "renders": 488,
+    "commits": 7,
+    "renders": 591,
     "requests": 2
   },
   "folder (revisit)": {
     "commits": 3,
-    "renders": 275,
+    "renders": 337,
     "requests": 1
   }
 }