I need an experienced DevOps professional to review and optimize the configuration of Cassandra DB integrated with Thingsboard, as we are experiencing unusually high system utilization. Additionally, our custom FASTAPI application, which interacts with the timeseries data for calculations, is either failing to return any data or doing so with significant delays. The work involves diagnosing and resolving issues across the stack, ensuring seamless performance. Proficiency in Thingsboard, Cassandra, FASTAPI, Kafka, Python, and Linux is essential. Please bring your expertise to this project as the resolution is required urgently.