fix(example): support multi-step Responses tool streaming

[abetlen]

Fix multi-step Responses tool streaming in the example server.

• Preserve custom tool format metadata for Responses streaming clients.
• Ignore unsupported built-in Responses tools when adapting tools for chat templates.
• Continue schema-derived leading-capture parsing after tool calls.
• Recover malformed Gemma-style tool argument wrappers before falling back to string arguments.

Validation:

• python3 -m py_compile examples/server/server.py
• Gemma 4 MTP server smoke-tested on tirgoviste.local with Codex single-step and multi-step shell tool calls.