test-kimi-k2: adjust for template's message splitting behavior
Kimi template splits messages into hist_msgs (up to last non-tool-call
assistant) and suffix_msgs (after). Both get `<think></think>` tags, but:
- hist_msgs: reasoning_content is discarded (empty think tags)
- suffix_msgs: reasoning_content is preserved
The needle tests use a single assistant message which becomes the "last
non-tool-call assistant" and goes to hist_msgs, so reasoning is discarded.
- Mark `supports_disable_thinking=No` since think tags are always output
- Skip run_template_test_suite for experimental impl (needle tests
incompatible with this message splitting)
Enables: kimi_k2:experimental
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>