manifests: push down expected node length into the parser This strictly enforces the node length in the manifest lines according to what the repository expects. One test case moves large hash testing into the non-treemanifest part as treemanifests don't provide an interface for overriding just the node length for now. Differential Revision: https://phab.mercurial-scm.org/D10533

core: don't hard-code node length Differential Revision: https://phab.mercurial-scm.org/D10536

core: don't hard-code hex node lengths Differential Revision: https://phab.mercurial-scm.org/D10535

enforcesinglehead-test: add the expected node output next to the error this make it simpler to validate that the test is correct. Differential Revision: https://phab.mercurial-scm.org/D10545

revlog: code for `revlogv0` in its own module This code is mostly unused compatiblity code. Yet it take a prohiminent place in the `revlog.py` module. That module is already quite big, so we move all that code in a dedicated module. Differential Revision: https://phab.mercurial-scm.org/D10511

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

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