delta-find: adjust the moment when we mark something as "tested" In a coming change, not all elements of `group` might get tested. So we need to have more control about when a revision is actually added to the `tested` set. So we move to a more verbose (and more fragile) version.

delta-find: rename a variable for clarity the index in the delta-chain is also the snapshot depth. So we rename the variable for clarity.

delta-find: small documentation update This is not a 1-1 mapping, but a 1-n mapping. Lets make the associated comment clearer.

delta-find: move pre-filtering with other pre-filtering logic This is more consistent and will help use to be in a clean state before dealing with the "too large group" issue. As a side effect, the debug output now skip some useless cases, making it more useful.

delta-find: expand a function definition and call before extendin it This make the next changeset more compact.

debug: add an option to display statistic about a unbundling operation This will helps a lot to understand how the bundling decision have actually impacted pull/unbundle on the other side.

debug: add an option to display statistic about a bundling operation This will helps a lot to understand how the bundling decision might impact pull/unbundle on the other side.

delta-find: add debug information about reuse of cached data This will help us to understand the behavior of find-delta during a pull.

tests: stop creating temporary files in TESTDIR

cffi: fix a bytes vs str issue on macOS when listing directories This code hasn't been touched in recent years, and the other implementation return bytes for the filename, so I assume this is a holdover from the py2 days. I was unable to test it on mac though, because the `_osutil` import failed.