View: build_usage answers how the build nodes are used in one call; the checker's tries name their asks

The operator's question (how much are the build nodes used, is ace eligible) took six calls over four tools.
build_usage reads it from the bus's states: seats held (have), capacity (mesh-config resolved), pauses, the
build modules' steps by kind with left-running keys, the last hour and day with total and median time and time
at capacity, the running tries, and the backlog the view program reads from the seats' streams. A try now names
the asks it put, and the checker announces its tries readable, so the view tells a try's asks from a check's.

modules/mesh-delivery-view/module.json

@@ -13,7 +13,8 @@
     "assigner_wants",
     "assigner_want",
     "assigner_differences",
-    "node_haves"
+    "node_haves",
+    "build_usage"
   ],
   "emits": [
     "delivered",
@@ -27,11 +28,19 @@
   "reads": [
     "mesh-controller.assignments",
     "mesh-controller.builds",
+    "mesh-build-go.pauses",
+    "mesh-build-go.steps",
+    "mesh-build-image.pauses",
+    "mesh-build-image.steps",
+    "mesh-build-node.pauses",
+    "mesh-build-node.steps",
+    "mesh-config.resolved",
     "mesh-controller.composed",
     "mesh-delivery-assigner.asks",
     "mesh-delivery-assigner.differences",
     "mesh-delivery-assigner.wants",
     "mesh-delivery-builder.builds",
+    "mesh-delivery-checker.tries",
     "mesh-delivery-gate.asks",
     "mesh-delivery-gate.source",
     "mesh-delivery-indexer.candidates",