Fix annotation scope, deadlock, MRO, and HEAPTYPE issues by youknowone · Pull Request #7087 · RustPython/RustPython

…7087)

* Fix annotation scope, deadlock, MRO, and HEAPTYPE issues

Annotation scope:
- Remove module-level annotation re-scan that created phantom
  sub_tables, breaking annotation closure for comprehensions
- Add async comprehension check in symbol table with
  is_in_async_context(); annotation/type-params scopes are
  always non-async
- Save/restore CompileContext in enter/exit_annotation_scope
  to reset in_async_scope

Deadlock prevention:
- Fix TypeVar/ParamSpec/TypeVarTuple __default__ and
  evaluate_default by cloning lock contents before acquiring
  a second lock or calling Python

Other fixes:
- Add HEAPTYPE flag to Generic for correct pickle behavior
- Guard heaptype_ext access in name_inner/set___name__/
  set___qualname__ with safe checks instead of unwrap
- Fix MRO error message to include base class names
- Add "format" to varnames in TypeAlias annotation scopes
- Fix single-element tuple repr to include trailing comma

* Unmark failing markers