fix(e2e): reject first listing that returns after the 40s deadline

A poll may start with remaining budget and still return after started+timeout
if the transport overruns its clamp. Recheck the first-listing deadline after
the response so a late listing does not open the continuous DB-sync phase

(cherry picked from commit 7ff2bcbf14)

tests/e2e/proxy_client.py

@@ -154,6 +154,8 @@ def await_servable(
         if not listed:
             first_seen_at = None
         elif first_seen_at is None:
+            if t > started + timeout:
+                return NotServable(last_result=last_result)
             first_seen_at = t
             if db_sync_seconds <= 0:
                 return Servable()