Name the build slice without a dash so it sits beside user.slice, and restart it when its limits change (issue 1798)

modules/build-agent/files/meshbuild.slice

@@ -0,0 +1,10 @@
+# Managed by the mesh (module build-agent). Replaced on every push; edit the module's settings instead.
+#
+# Everything a build or check starts on this machine runs in this slice (novox/hq issue 1798): the build
+# agent starts every container with --cgroup-parent=meshbuild.slice. The weights only bind while the machine
+# is busy, so an idle machine still builds at full speed; the memory limits are the part that always binds.
+[Slice]
+CPUWeight=${setting:cpu-weight}
+IOWeight=${setting:io-weight}
+MemoryHigh=${setting:memory-high}
+MemoryMax=${setting:memory-max}