chore: regenerate libraries with gapic-generator @ eb8a7662 - #18855

@parthea For the Spanner test fix, can we initialize self._client_options as a real ClientOptions object inside _Client.__init__ instead of setting _client_options = None in test_spanner_api_experimental_host?

Why ClientOptions seems like a better idea here:

1. No truthy/mock surprises: With an unspec'ed Mock, reading any unset attribute (like tracer_provider or future ClientOptions fields) returns a truthy child Mock instead of None. A real ClientOptions object naturally defaults unset fields to None.
2. Avoids shared-state mutation: _Instance.__init__ uses a shared default client=_Client() across tests, so setting database._instance._client._client_options = None in one test mutates _client_options for subsequent tests.
3. Less boilerplate: It replaces 9 lines of manual None assignments and matches self._client_info = gapic_v1.client_info.ClientInfo() right above it.

Files and Lines to Update

1. packages/google-cloud-spanner/tests/unit/_async/test_database.py

• Line 2643 (test_spanner_api_experimental_host): Remove database._instance._client._client_options = None.
• Lines 4292–4309 (_Client.__init__): Replace the CrossSync.Mock() setup with ClientOptions:

        from google.api_core.client_options import ClientOptions
        from google.cloud.spanner_v1 import ExecuteSqlRequest

        self.project = project
        self.project_name = "projects/" + self.project
        self._endpoint_cache = {}
        self.database_admin_api = _make_database_admin_api()
        self.instance_admin_api = _make_instance_api()
        self._client_info = gapic_v1.client_info.ClientInfo()
        self._client_options = ClientOptions(
            api_endpoint="spanner.googleapis.com",
            universe_domain="googleapis.com",
        )
        self._experimental_host = None

2. packages/google-cloud-spanner/tests/unit/test_database.py

• Lines 3713–3730 (_Client.__init__): Apply the same change to the sync helper:

        from google.api_core.client_options import ClientOptions
        from google.cloud.spanner_v1 import ExecuteSqlRequest

        self.project = project
        self.project_name = "projects/" + self.project
        self._endpoint_cache = {}
        self.database_admin_api = _make_database_admin_api()
        self.instance_admin_api = _make_instance_api()
        self._client_info = gapic_v1.client_info.ClientInfo()
        self._client_options = ClientOptions(
            api_endpoint="spanner.googleapis.com",
            universe_domain="googleapis.com",
        )
        self._experimental_host = None

Fixed in 0f4029b in PR #18955