.Net: Add Gemini usage metadata CachedContentTokenCount and ThoughtsTokenC… #27872

Job	Run time
paths-filter	8s
Python Pre-Merge Integration Tests - AI Services (incl samples using those)	0s
Python Pre-Merge Integration Tests - Ollama	0s
Python Pre-Merge Integration Tests - Agents	0s
Python Pre-Merge Integration Tests - Memory (incl samples using those)	0s
Python Integration Tests - Scheduled run	0s
python-integration-tests-check	4s
Python Pre-Merge Integration Tests - Multi-Modality	0s
	12s

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