Fold the transient/permanent sync-loop tests into one parametrized table
and add the two classifier branches that had no loop-level coverage: a
401 whose body was rewritten to HTML by a reverse proxy (errcode dropped,
so only http_status can stop the loop) and a 429 M_LIMIT_EXCEEDED that
must be retried because neither errcode nor status is an auth signal.
Deleting the http_status fallback in _is_permanent_matrix_auth_error now
fails the 401-html case.
Hoist _sync_error to module level so parametrize can call it directly
instead of the staticmethod.__func__ workaround. Trim the
test_ws_auth_retry docstring, which still described a Matrix test class
that moved to test_matrix.py.
935cc237db