obshashtree: move obshashtree in its own module The code no longer serve a core purpose. We just keep it because the command might be useful. We move it in a dedicated module so that it does not get in the way of other work.

obsdiscovery: drop `obshash` discovery protocol (issue6136) The protocol has been superseeded by stablerange for a long time. It is untested and more and more buggy. Since this is deprecated experimental code in an experimental code, we drop it. We keep the underlying computation and debug command around for now. They might still be useful to looks at repositories

cmdrewrite: use context manager for some locks and transactions These were the trivial cases where I didn't even need to extend the scope of a transaction or change indentation to fix it.