fix: add kimi/moonshot to Anthropic tool thinking history normalizer (#3377)

* fix: add kimi/moonshot to Anthropic tool thinking history normalizer

Kimi's Anthropic-compatible endpoint requires reasoning_content in
assistant tool call messages when thinking is enabled, same as DeepSeek.
The is_reasoning_content_compatible_identifier already included kimi/moonshot
but is_anthropic_tool_thinking_history_identifier was missing them, causing
400 errors on multi-turn conversations with tool calls.

Closes #3351

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* refactor: unify reasoning vendor hints into a single SSOT list

Replace the two separately-maintained vendor identifier lists with one
shared REASONING_VENDOR_HINTS constant and a single
is_reasoning_vendor_identifier predicate. The Anthropic
tool-thinking-history matcher and the openai_chat reasoning_content
matcher previously kept independent lists, which is exactly how
kimi/moonshot ended up in one but not the other (#3351). A single source
of truth keeps the two from drifting apart again.

Also add a Kimi regression test for the Anthropic tool-history
normalization path.

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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: Jason <farion1231@gmail.com>