- Added _parse_xml_style_tool_calls() method to parse XML format like:
  <tool><name>search</name><arguments>{...}</arguments></tool>
- Modified extract_tool_calls() to use XML parsing as fallback
- ToolCallParser now serves as fallback for all specific model parsers
  via ModelParserAdapter (QwenParser, DeepSeekParser, LlamaParser,
  MistralParser, ClaudeParser, CommandRParser, GemmaParser, GrokParser,
  PhiParser, ApexBig50Parser)