FastAPI Performance: Fixing Auth, Crypto, and Serialization Bottlenecks

A developer's deep dive into FastAPI performance reveals that offloading CPU-bound Argon2id to a ThreadPoolExecutor prevents event loop blocking. Switching from RSA-2048 to Ed25519 for signing tokens speeds up signing but slows verification, mitigated by caching. Using msgspec for serialization can be up to 5x faster than Pydantic, reducing CPU load on data-heavy responses.