Builder: count only deliverable asks ahead, drop the old message of an ask asked again, and read a seat's queue (issue 1945)

mesh-delivery #51's re-ask never fired for mesh-build-node.4e7b118e: messages the
SEAT_NODE_BUILD_GO workers had given up on stay on the work queue, and each counted
as waiting ahead, so the ask was never asked again (note 62). A message ahead now
waits only when no node wrote its step and no ask of its kind asked after it was
taken; the old message of an ask asked again is deleted from its stream; and
builder_seat_queue (answered by the builder through its queues state, as only its
account may read the stream) shows each message and whether it still waits.

modules/mesh-delivery-builder/module.json

@@ -4,6 +4,7 @@
   "slug": "builder",
   "tools": [
     "builder_ask_again",
+    "builder_seat_queue",
     "builder_stuck"
   ],
   "emits": [
@@ -20,6 +21,7 @@
   "state": [
     { "name": "builds", "history": 5 },
     { "name": "instances", "history": 1 },
+    { "name": "queues", "history": 1 },
     { "name": "reasks", "history": 1 }
   ],
   "reads": [