Each insert, delete and rescore update was its own commit to disk, so a
resync of about a thousand QSOs froze the window thread. LogStore has a
new Batch() scope that commits its writes together. ContestSession uses
it in AddRangeFromNetwork, ClearFromNetwork and Rescore.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>