deepseek-r1: fix tool call parsing with trailing whitespace
- Use `additional_stops` instead of inline `consume_eos()` pattern
- Add `p.space()` after JSON args to handle model's trailing whitespace
- Restructure parallel tool calls handling for cleaner parsing
- Add test case matching server test scenario
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
