blackbox: extract function to test if log event is tracked This will be a required method of the logger interface.

blackbox: initialize inlog flag properly And ditch the "bb" prefix as it's no longer a ui extension class.

blackbox: initialize repo attribute properly And ditch the "bb" prefix as it's no longer a ui extension class.

blackbox: unindent "if True" block

blackbox: extract logger class from ui wrapper This moves most functions to new blackboxlogger class. The ui wrapper will be removed later.

blackbox: rename variables to prepare extracting core logic from ui wrapper I'm going to add ui.setlogger() function so that I can enable logging feature in command server without extending ui.__class__. This prepares for it. "self" will be a logger instance, so this patch renames some of them to "ui".

sparse-revlog: rework the way we enforce chunk size limit We move from a O(N) algorithm to a O(log(N)) algorithm. The previous algorithm was traversing the whole delta chain, looking for the exact point where it became too big. This would result in most of the delta chain to be traversed. Instead, we now use a "binary" approach, slicing the chain in two until we have a chunk of the appropriate size. We still keep the previous algorithm for the snapshots part. There are few of them and they are large bits of data distant from each other. So the previous algorithm should work well in that case. To take a practical example of restoring manifest revision '59547c40bc4c' for a reference NetBeans repository (using sparse-revlog). The media time of the step `slice-sparse-chain` of `perfrevlogrevision` improve from 1.109 ms to 0.660 ms.

doctest: add a `issnapshot` method to _testrevlog We'll need it soon.