test(v2): Add sync/async interface parity tests

- Use AST parsing to compare method sets and parameter signatures between sync and async classes
- Verify mechanically copied method bodies remain consistent after stripping async syntax
- Maintain exemption list for structural differences like sync vs async generators
- Implement auto-discovery mechanism to ensure all new async twins are covered by tests
- Add guard tests to verify detectors accurately catch missing methods or parameter drift
- Exclude legacy SDK and standalone submodule directories to prevent false positives

Author: luk384090-cloud

tests/v2/__init__.py

@@ -0,0 +1,9 @@
+# -*- coding: utf-8 -*-
+# Copyright (c) Alibaba, Inc. and its affiliates.
+"""Checks on the v2 SDK tree as a whole, rather than on one module.
+
+These tests read the shipped source and assert structural invariants across
+it -- the sync/async twins expose the same contract, that sort of thing.
+They have no runtime counterpart to import, so they live apart from the flat
+per-module suites in ``tests/``.
+"""