Platform updates prepare in about two minutes instead of twenty

When the platform updates itself, it first rebuilds every dynamic content type against the new version. That preparation deliberately paced itself so a busy portal would not slow down — but during an update the preparing side isn't serving anyone yet, so the pacing only made updates take longer. Measurements showed the actual rebuild work takes under a minute; the pacing accounted for most of the wait.

Preparation now runs at full speed during an update and keeps its gentle pacing only when a running portal warms itself in the background. Updates get ready in a couple of minutes, and day-to-day editing and compiling of individual types is unchanged.