ruff

0529ad67 - [red-knot] Internal refactoring of visibility constraints API (#15913)

[red-knot] Internal refactoring of visibility constraints API (#15913) This extracts some pure refactoring noise from https://github.com/astral-sh/ruff/pull/15861. This changes the API for creating and evaluating visibility constraints, but does not change how they are respresented internally. There should be no behavioral or performance changes in this PR. Changes: - Hide the internal representation isn't changed, so that we can make changes to it in #15861. - Add a separate builder type for visibility constraints. (With TDDs, we will have some additional builder state that we can throw away once we're done constructing.) - Remove a layer of helper methods from `UseDefMapBuilder`, making `SemanticIndexBuilder` responsible for constructing whatever visibility constraints it needs.