rust-dirstate: fall back to v1 if reading v2 failed This will help us not fail when a v1 dirstate is present on disk while a v2 was expected (which could happen with a racy/interrupted upgrade).

dirstate: add test showing dirstate version mismatch causes an error We should fall back to trying dirstate v1 when v2 fails to read.

rust-dirstate: rename `has_dirstate_v2` to `use_dirstate_v2` It is closer to the right semantics. I added a docstring to better explain the reasonning. In the next patch(es), I will address the underlying issue of finding the "wrong" version of the dirstate on disk.

delta-find: fix pulled-delta-reuse-policy=forced behavior The code that select delta still has too many oportunity to discard the delta is has been forcibly asked to reuse. However is is fairly easy to use a dedicated fastpath for this case. So we do so. Cleaning other code that tries to enforce that policy will be done on default.

delta-find: display more information about the search in some case This will be useful to access the effect of the delta reuse policy.

deltafind: issue debug information when we fast-path rivial case too More debug options never hurts.

delta-find: gather the condition to blindly use a full snapshot together We are about to make the `if` body bigger, so having only one of them is simpler/

delta-find: initialize the debug information much sooner (when possible) This help us to record debug information in alternative path.

delta-find: fix `parents` round detection We should compare integer with integer, instead of bytes (node).

delta-find: intrduce a `_one_dbg_data` method This helps with the initialisation of the expected debug information.

delta-find: move final debug processing in a `_dbg_process_data` method This will help us making sure we can call the necessary debugging code in alternative codepath.

delta-fine: use the `_debug_search` attribute directly By adjusting the value at creation time, we can avoid the need to use and intermediate variable.

delta-find: move the `gather_debug` logic in a property This will make it simpler to get be reused in multiple places.

tests: check `pulled-delta-reuse-policy=forced` without general delta If general delta is not available, the amount of delta we can reuse at all will be more limited. We check that application still work and does not corrupt the repository.

tree-manifest: allow `debugupgraderepo` to run on tree manifest repo There does not seems to be anything wrong with running the current logic on them. So we remove the limitation.