In astral-sh/ruff#20128, we disabled boundness analysis for implicit instance attributes:

class C:
    def __init__(self):
        if False:   
            self.x = 1

C().x  # would previously show an error, with this PR we pretend the attribute exists

It is possible that we can simply re-enable this now that we have a better strategy for dealing with these cyclic type inference problems.

We probably don't want a full-blown revert of that PR. I like TypeQualifiers::IMPLICIT_INSTANCE_ATTRIBUTE much better than TypeQualifiers::POSSIBLY_UNBOUND_IMPLICIT_ATTRIBUTE, so maybe we can prevent bringing the latter back.

For some reason, I don't see any regression tests for #758 in that PR, so we should probably add them when we resolve this issue.