New Features

• Add an MCP server to the gateway exposing its API in /mcp.
• Report provider prompt caching statistics via API and UI.
• Report usage statistics (e.g. tokens, latency, cost) for inference evaluations via CLI tool, API, and UI.
• Add the Prometheus metrics tensorzero_input_tokens_total and tensorzero_output_tokens_total.
• Add configuration field content_type_overrides to handle file inputs for long-tail providers.

& multiple under-the-hood and UI improvements