The bus module sets and restores a key-value bucket's expiry (ADR 0582)

nats_bucket_expiry reads a bucket's stream, sets MaxAge (a duration, or none), reads it back, records a hand act
through mesh-hand-acts and says bucket-expiry-set, so the lease write can take the 15 seconds off the lease bucket and
the hand-back can restore them. Refuses a missing why and a name that is no bucket. Two new unit tests (stand-in
embedded server) in a module at 26 of 500; no test removed, none needed to stay in budget.

(issue 774, 774/S6)

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

modules/nats/module.json

@@ -31,7 +31,11 @@
   "emits": [
     "consumer-removed",
     "bucket-keys-removed",
-    "stream-removed"
+    "stream-removed",
+    "bucket-expiry-set"
+  ],
+  "invokes": [
+    "seat:mesh-hand-acts.hand-act"
   ],
   "consumes": [],
   "listens": [
@@ -56,7 +60,8 @@
     "nats_snapshot_verify",
     "nats_consumer_remove",
     "nats_bucket_remove",
-    "nats_stream_remove"
+    "nats_stream_remove",
+    "nats_bucket_expiry"
   ],
   "guards": [
     8222