changegroup: rename cg1packer to cgpacker There is now only a single class. We don't need to encode the version in its name since the version is a lie. Differential Revision: https://phab.mercurial-scm.org/D4084

changegroup: control delta parent behavior via constructor The last remaining override on cg2packer related to parent delta computation. We pass a parameter to the constructor to control whether to delta against the previous revision and we inline all parent delta logic into a single function. With this change, cg2packer is empty, so it has been deleted. Differential Revision: https://phab.mercurial-scm.org/D4083

changegroup: control reordering via constructor argument cg2packer.__init__ exists just to override self._reorder. Let's parameterize this behavior via an argument to the parent's __init__. The logic for self._reorder is kinda wonky. None is used as a special value and the value should be None in some situations. It is probably worth rewriting this logic to make behavior more explicit. This will likely happen as part of future work to control the delta generation process that I have planned. Differential Revision: https://phab.mercurial-scm.org/D4082

changegroup: consolidate tree manifests sending into cg1packer Previously, we overrode a method to control how manifests were serialized. This method was redefined on cg3packer to send tree manifests. This commit moves the tree manifests sending variation to cg1packer and teaches the cgpacker constructor to control which version to use. After these changes, cg3packer was empty. So it has been removed. Differential Revision: https://phab.mercurial-scm.org/D4081

changegroup: pass end of manifests marker into constructor cg3 inserts a custom marker in the stream once all manifests have been transferred. This is currently abstracted out by overriding a method. Let's pass the end of manifests marker in as an argument to avoid the extra method. Differential Revision: https://phab.mercurial-scm.org/D4080

changegroup: pass function to build delta header into constructor Previously, the delta header struct format was defined on each class and each class had a separate function for building the delta header. We replace both of these with an argument to __init__ containing a callable that can format a delta header given a revisiondelta instance. Differential Revision: https://phab.mercurial-scm.org/D4079

changegroup: make delta header struct formatters actual structs Why we weren't using compiled Struct instances, I don't know. They make code simpler. In theory they are faster. Although I don't believe I was able to measure any meaningful change. That could be because this code is often dominated by compression, deltafication, and function call overhead. Differential Revision: https://phab.mercurial-scm.org/D4078

changegroup: pass version into constructor Currently, the version is an attribute on each class. Passing the argument into the constructor gets us one step closer to eliminating cg2packer and cg3packer. Differential Revision: https://phab.mercurial-scm.org/D4077