Bump version to 0.2.0

[meshy]

The changelog for this version reads:

Added

• Django 6.0 has been added to the test matrix.
• In tests, an error will now be raised when opening a transaction if there are pre-existing unhandled after-commit callbacks. The pre-existing callbacks would previously run when transaction exits. This helps catch order-of-execution bugs in tests. The error can be silenced by setting the SUBATOMIC_CATCH_UNHANDLED_AFTER_COMMIT_CALLBACKS_IN_TESTS setting to False to facilitate gradual adoption of this stricter rule.
• The transaction, transaction_required and transaction_if_not_already decorators can now be used without parentheses. Fixes Don't require parentheses for decorator calls #103.

Fixed

• Ensure cleanup actions in durable always happen when the wrapped code raises an unexpected error.

Removed

• _contextmanager_without_decorator, _NonDecoratorContextManager, NotADecorator.
  These implementation details were not intended to be a part of our public API.