0f18a08a0a
## Summary This PR implements the strategy described in https://github.com/astral-sh/ty/issues/1871: we iterate over the positive types, resolve them, then intersect the results.
Markdown files within the mdtest/ subdirectory are tests of type inference and type checking;
executed by the tests/mdtest.rs integration test.
See crates/ty_test/README.md for documentation of this test format.