fix(runners): preserve caller container configuration when adopting response ID (#1988)

[iosayin]

Fixes #1988

Summary

Previously, both sync and async tool runners unconditionally set self._params["container"] = last_assistant_message.container.id. This had two negative side-effects:

1. If the caller provided a dictionary with skills (e.g. {"skills": [...]}), adopting the server ID completely converted the parameter into a raw string, dropping the configured skills on subsequent turns.
2. If the caller pinned an explicit container ID (or string), the response's container ID could overwrite the caller's explicit configuration.

Changes

• Added helper _update_container_from_response in src/anthropic/lib/tools/_beta_runner.py:
  • If caller provided no container (or None), it sets the server container ID.
  • If caller provided a container dictionary, it adopts the server container ID under id while preserving any existing properties such as skills. If caller already had an explicit id, it preserves the caller's ID.
  • If caller provided an explicit string ID, it preserves the caller's pinned string ID.
• Updated BaseSyncToolRunner and BaseAsyncToolRunner to invoke _update_container_from_response.
• Added unit tests in tests/lib/tools/test_runners.py verifying that container skills and caller-pinned IDs are preserved across runner turns.