Important

Migrates model count functionality to gateway, adding a new endpoint and updating client and server code.

• Behavior:
  • Adds /internal/models/count route in internal.rs to gateway, handled by count_models_handler.
  • Removes countDistinctModelsUsed from DatabaseClient in internal/tensorzero-node/src/database.rs.
  • Updates TensorZeroClient in tensorzero.ts to use new endpoint for model count.
• Types:
  • Adds CountModelsResponse type in CountModelsResponse.ts and types.rs.
• Tests:
  • Adds E2E test test_count_models_endpoint in models.rs to verify new endpoint.

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