Part of astral-sh/ty#994 ## Summary Add new special forms to `ty_extensions`, `Top[T]` and `Bottom[T]`. Remove `ty_extensions.top_materialization` and `ty_extensions.bottom_materialization`. ## Test Plan Converted the existing `materialization.md` mdtest to the new syntax. Added some tests for invalid use of the new special form.
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.