Sync minja vendor: ReasoningFormat detection and tojson separators
- Rename requires_typed_content → requires_typed_content_blocks
- Rename ReasoningFormat enum values for clarity
- Add tojson(separators=...) support for Kimi K2 template
- Sync from https://github.com/google/minja/pull/89
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>