ruff

811f78d9 - [red-knot] small efficiency improvements and bugfixes to use-def map building (#12373)

[red-knot] small efficiency improvements and bugfixes to use-def map building (#12373) Adds inference tests sufficient to give full test coverage of the `UseDefMapBuilder::merge` method. In the process I realized that we could implement visiting of if statements in `SemanticBuilder` with fewer `snapshot`, `restore`, and `merge` operations, so I restructured that visit a bit. I also found one correctness bug in the `merge` method (it failed to extend the given snapshot with "unbound" for any missing symbols, meaning we would just lose the fact that the symbol could be unbound in the merged-in path), and two efficiency bugs (if one of the ranges to merge is empty, we can just use the other one, no need for copies, and if the ranges are overlapping -- which can occur with nested branches -- we can still just merge them with no copies), and fixed all three.