check in Rust parser whether string candidates are valid dotted names

[tdyas]

As reported in #20324, the Rust dependency inference parser does not check whether string candidates (when string_imports = true is in effect) are valid dotted Python names.

While the Python-side of the dependency inference logic does now check (as of #20472), it is easy enough to support this in Rust using the tree-sitter grammar.

[cognifloyd]

Like like there's a loop or a hang or a race condition, add lint failed miserably.

Wait for green ci