Fix mypy type errors for database_api integration

- common_helpers.py: Handle str->datetime conversion for time field
- sync_handle.py: Add type: ignore for get_dynamic_global_properties return
- init_node.py: Add type: ignore for VestPrice.from_dgpo arg
- wallet_api.py: Add type: ignore for owner_auths return
- node_handle_base.py: Remove unnecessary Time.parse call (get_head_block_time already returns datetime)