Tool calling polish: streaming docs, error consistency, typing

[Kamilbenkirane]

Priority: Low
Related: #199

Minor polish items:

• OpenResponses streaming: _response_data pattern is an undocumented workaround for late-arrival data — add docstring explaining why
• Streaming override: Tool call parsing not cleanly overridable via virtual method hook in protocol base classes
• Schema name generation: TextFormatMapper uses inner_type.__name__ which could fail if type lacks __name__

Files:

• src/celeste/modalities/text/providers/openresponses/client.py:53-69
• src/celeste/modalities/text/protocols/chatcompletions/client.py
• src/celeste/protocols/openresponses/parameters.py:60

[Kamilbenkirane]

First item resolved by #219 (file deleted, protocol version has docstrings). Second and third are non-issues.