Give the build modules' steps state an age of two days, and keep a node's pause in a pauses state of its own

mesh-build-go's steps bucket filled to the bus's 64 MiB cap (27,370 keys, none ever removed) and
refused the end of a passed check, so the check read failed; mesh-build-node's (17.8 MB) and
mesh-build-image's grow the same way. A step's key is per step: its reader reads its end within
the step's bound, and a check's verdict is kept by the checker, so two days is ample. The node's
pause key lived in the same bucket and would have ended by itself; it moves to a pauses state
without an age (mesh-sdk fix/steps-bucket-ages, Puller.PausePut). No node is paused today, so
nothing is carried over.

modules/mesh-build-node/cmd/mesh-build-node/main.go

@@ -46,6 +46,8 @@ func main() {
 		Emit:                func(t string, b any) error { return stdio.Emit(t, b) },
 		Steps:               stdio.State(delivery.StepsState).Put,
 		ReadSteps:           readOf(stdio.State(delivery.StepsState)),
+		Pauses:              stdio.State(delivery.PausesState).Put,
+		ReadPauses:          readOf(stdio.State(delivery.PausesState)),
 		ReadToolchainsState: readOf(stdio.State(delivery.ToolchainsState)),
 		Work:                WorkDir,
 		Run:                 forgekey.ExecRunnerClean(0),