chat: migrate functionary_v3_1_llama_3_1 to modular PEG parser
Move Functionary v3.1 (Llama 3.1 style) tool call parsing to
common/chat-syntax/functionary-v3-1-llama-3-1.cpp.
Uses native PEG parser for format:
<function=name>{...}</function>
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>