discovery: stop direct use of attribute of partialdiscovery Instead of accessing `undecided` directly for ui display purposes, we introduce a `stats()` method that could be extended in the future with more interesting information. This is in preparation for a forthcoming Rust version of this object. Indeed, attributes and furthermore properties are a bit complicated for classes in native code. We could go further and rename `undecided` to mark it private, but `_undecided` is already taken as support for `_undecided` lazyness.