obscache: use the smaller scope function This make the function simpler and allow larger update on the 'upgradeneeded' one.

obscache: extract the cache key validation in its own function This help keep the "up to date logic" simpler and prepare a more complex version of the "upgradeneeded" logic that would return the full data needed for the upgrade.

obshistory: use formatter instead of ui.write in the debugobshistory command Replace ui.write with a formater to have template support and json output. Update tests to assert json outputs.