Resolve const-block conflict in openai_gateway_grok_cache.go: keep #4590's client tool cache constants, drop grokFreeRolling24hTokenLimit (moved to pkg/xai as IsGrokFreeRolling24hTokenLimit with legacy 2M support).
Resolve const-block conflict in openai_gateway_grok_cache.go: keep #4590's client tool cache constants, drop grokFreeRolling24hTokenLimit (moved to pkg/xai as IsGrokFreeRolling24hTokenLimit with legacy 2M support).