discovery: introduce a partialdiscovery object...
discovery: introduce a partialdiscovery object
This object will ultimately gather the data about common, undecided and
missing revs in a single place and deal with most graph related computations.
The goal is both to clarify the algorithm and to help provides a simple and
clear API that can be reimplemented in Rust.
For now, we only moved the `common` set in the object. In this commit, some
direct access to the "private" `disco._common` attribute persist. They have
not been removed yet because we won't need to expose a full API identical to
`incrementalmissingancestors` and it seems simpler to access the attribute
directly until the replacement is in place.
