upgrade: no longer keep all revlogs in memory at any point Keeping all object open is unsustainable, so we will open them on demand. This mean opening them multiple times, but this is a lesser evil. Each revlog consume a small amount of memory (index content, associated nodemap, etc). While there are few "big" revlog, the sheer amount of small filelog can become a significant issue memory wise, consuming multiple GB of memory. If you combines this extra usage with the use of multiprocessing, this usage can quickly get out of control. This can effectively block the upgrade of larger repository. This changeset fixes this issue.

tests: remove non-python3 line matching and tests block We don't support Python2 anymore

demandimport: convert ignored modules from bytes -> str in extensions The default list of ignored modules are str, and test for bypassing the lazy import is `module.__name__ in ignores`, so these were effectively NOT ignored. Most of these date back to the grand byteification in 687b865b95ad, with some subsequent additions that followed the existing example. I have no idea if these modules in fact need to bypass lazy importing, but at least it follows the intent of the code.

dirstate-v2: fix edge case where entries aren't sorted See previous commit for more details.

dirstate-v2: highlight a bug when Python-packed but used in `rhg` The Python packer creates unsorted entries in the edge case that a file starts with the same name as a sibling folder. This bug has no effect on the Python `hg status` since Python ignores directories. `rhg` assumes that all on-disk entries are sorted (which is a property of the format) including folder, hence the issue highlighted. This is also technically broken in Rust-augmented `hg status`, but it makes setting up the test more complex than necessary, since it requires the packing to be Python only (which it isn't if you have Rust extensions). Fix is in the next commit.

dirstate-v2: correct documented return values of `pack_dirstate`

dirstate-v2: fix typos in docstrings

dirstate-v2: update constant that wasn't kept in sync Despite the best efforts of the comment, this constant wasn't kept in sync when the flags were being rewritten. The fact that this doesn't actually break anything in the Rust implementation too much (which does use directories) relies on the fact that all nodes can have children and that dirstate traversal is not based on that flag, but for metadata in optimizations. However the bug could become more serious should we start encoding stronger guarantees using a combination of flags including this one.

lfs: avoid closing connections when the worker doesn't fork Probably not much more than an minor optimization, but could be useful in the case of `hg verify` where missing blobs are fetched one at a time.

lfs: fix blob corruption when tranferring with workers on posix The problem seems to be that the connection used to request the location of the blobs is sitting in the connection pool, and then when workers are forked, they all see and attempt to use the same connection. This garbles everything. I have no clue how this ever worked reliably (but it seems to, even on Linux, with SCM Manager 1.58). See previous discussion when worker support was added[1]. It shouldn't be a problem on Windows, since the workers are just threads in the same process, and can see which connections are marked available and which are in use. (The fact that `mercurial.keepalive.ConnectionManager.set_ready()` doesn't acquire a lock does give me some pause though.) [1] https://phab.mercurial-scm.org/D1568#31621