fix: honor Conversation.visualize options

[avinashgola]

Summary

• forward use_color and merge_audio_tokens from Conversation.visualize()
• disable ANSI escape sequences when use_color=False
• collapse consecutive audio-pad tokens while preserving loss-label boundaries
• add focused regression tests for both options

Testing

• python -m pytest tests/test_visualization.py -v (3 passed)
• ruff check fish_speech/content_sequence.py tests/test_visualization.py
• ruff check --ignore F401 fish_speech/conversation.py
• ruff format --check fish_speech/content_sequence.py fish_speech/conversation.py tests/test_visualization.py
• git diff --check

Fixes #1325

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