fix(python): allow type predicates in return annotations

[hechibing]

Fixes #424

Changes:

• Add a Python snippet parse context for return type annotations, so type predicates can compare return types against snippets like List
• Add a regression test for matching a type predicate on a Python return annotation

Verification:

• (Not run locally) cargo test -p marzano-core python_match_type_predicate_on_return_annotation

[hechibing]

Verification (Windows):

• cargo test -p marzano-core --no-default-features --features grit-parser,language-parsers,non_wasm python_match_type_predicate_on_return_annotation

Notes:

• Fix required keeping wrapper nodes (like Python ype in return annotations) when compiling snippets, so List can match a ype node.