DM-22093 added a "Task finished" timestamp to the metadata for all verify timing metrics. This inadvertantly caused the timestamps to be treated as tags in SQuaSH (see attached image), and will eventually bog down the server.

Change the timestamps from metadata to extras, which are not uploaded to SQuaSH. This is a breaking change, and will make accessing the data a bit clunkier:

measurement.notes["end"]

measurement.extras["end"].quantity  # yes, still a `str`