Refactor tool-call parsing for model-family-specific formats

[michalharakal]

Summary

Refactor parser support so family-specific output can be handled cleanly.

Scope

• Review whether ToolCallParser should remain generic or become pluggable
• Keep common parsing logic shared where possible
• Allow model-family-specific parsing to be registered cleanly

Acceptance criteria

• Parser handles current supported formats
• Family-specific parsing can be added without parser duplication