revlog: have an explicit "pack_header" method
Having to pass the version header when retrieving the binary version of every
single entry is a bit silly. So we extract that special logic in its own method.
This also prepare the move to newer revlog format, not storing the header within
an actual entry…
Differential Revision: https://phab.mercurial-scm.org/D10510
Pierre-Yves David <pierre-yves.david@octobus.net> [Sat, 01 May 2021 14:47:39 +0200] rev 47077
revlog: remove the revlogio class
The class only contains a single `parseindex` method. Lets just make it a
function and remove the `revlogio` class. It served us well but became thinner
and thinner overtime.
Differential Revision: https://phab.mercurial-scm.org/D10509