bug: _update_token_loop broken on async AbstractExpiringTokenCredentials

[malik89303]

Bug Report

YDB Python SDK version:

3.18.10

Environment

Current behavior:

ydb.aio.credentials.AbstractExpiringTokenCredentials provides ability to create async token provider with async auth_metadata

async def auth_metadata(self):
    return [(credentials.YDB_AUTH_TICKET_HEADER, await self.token())]

but update_token_loop expects sync auth_metadata

future: <Task finished name='update_token_loop' coro=<WriterAsyncIOStream._update_token_loop() done, defined at contrib/python/ydb/py3/ydb/_topic_writer/topic_writer_asyncio.py:686> exception=TypeError("'coroutine' object is not iterable")>
Traceback (most recent call last):
  File "contrib/python/ydb/py3/ydb/_topic_writer/topic_writer_asyncio.py", line 689, in _update_token_loop
    await self._update_token(token=self._get_token_function())
                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "contrib/python/ydb/py3/ydb/credentials.py", line 42, in get_auth_token
    for header, token in self.auth_metadata():
                         ^^^^^^^^^^^^^^^^^^^^
TypeError: 'coroutine' object is not iterable",

Expected behavior:

_update_token_loop works fine with async auth_metadata

Steps to reproduce:

1. create async ydb.aio.Driver with credentials instance of class inherited from ydb.aio.credentials.AbstractExpiringTokenCredentials

class SomeCredentialsProvider(ydb.aio.credentials.AbstractExpiringTokenCredentials):
    ...
    async def _make_token_request(self) -> dict[str, int | str]:
        token = await self._do_something()
        return {
            "expires_in": 1234,
            "access_token": token,
        }

2. create async TopicReader / TopicWriter
3. wait until _update_token_loop executes

Related code:

Other information: