Detect new syntax errors in type annotations for Python 3.14

Python 3.14 implements deferred evaluation of type annotations. It also imposes some new syntax restrictions on type annotations. In particular, it doesn't allow walrus operators or `await` keywords in annotations. These are not allowed by the typing spec within a type annotation, so pyright already reports these as invalid type annotations, but `Annotated` type arguments (other than the first) are exempt from this check.

Read the existing invalid type-annotation handling, focusing on how Annotated arguments are treated differently from other annotation expressions. Verify that walrus operators and await are rejected in every relevant annotation position, while valid Annotated metadata remains accepted.

Written by the indexing model from the issue text.