rewrite: simplify the `retained_extras` extra logic First, we move the definition of value outside of the rebase extensions, as this apply to all rebase-like operation and some live in other place (like evolve). Second we make it a simple set, so that it is easy for an extension to add a new value in it. Third, we move the associated logic in core too. That make it easily available to other extensions. Fourth we simplify it usage, as the verbose version of the filtering is just a handful on line long, we are just going to test all the value for updates, so the Projection overlay is not bringing much here. Note that, we make it a module level set, is a key is worth preserving it is probably worth preserving in all cases. This was already the behavior prior to this change.

stream-clone: smoothly detect and handle a case were a revlog is split This detect and handle the most common case for a race condition around stream and revlog splitting. The one were the revlog is split between the initial collection of data and the time were we start considering stream that data. In such case, we repatch an inlined version of that revlog together when this happens. This is necessary as stream-v2 promised a specific number of bytes and a specific number of files to the client. In stream-v3, we will have the opportunity to just send a split revlog instead. Getting a better version of the protocol for stream-v3 is still useful, but it is no longer a blocket to fix that race condition. Note that another, rarer race condition exist, were the revlog is split while we creating the revlog and extracing content from it. This can be dealt with later.

stream-clone: implement decidated `get_streams` method for revlog For revlog, we can do better using the maximum linkrev expected. This approach open the way to dealing with a much larger set of non-trivial changes, like splitting of inline revlogs. We will actually tackle this issue in the next changesets (thanks to this one).