obsstore: also guard agains changing object in '_checkkey' The 'upgradeneeded' function needs to be able to pass the object it fetched once.

obscache: guard from changing changelog or obsstore object We access these object once to make sure they will never change through the function (and their content will be fixed).

obscache: return the new data along-side the upgrade needs (and cache key) Having one function returning consistent data will help prevent race.

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.