Allow sys.path modifications between imports (#9047)

## Summary

It's common to interleave a `sys.path` modification between imports at
the top of a file. This is a frequent cause of `# noqa: E402` false
positives, as seen in the ecosystem checks. This PR modifies E402 to
omit such modifications when determining the "import boundary".

(We could consider linting against `sys.path` modifications, but that
should be a separate rule.)

Closes: https://github.com/astral-sh/ruff/issues/5557.

crates/ruff_python_semantic/src/analyze/mod.rs

@@ -1,4 +1,5 @@
 pub mod function_type;
+pub mod imports;
 pub mod logging;
 pub mod type_inference;
 pub mod typing;