Core types and traits for fastapi_rust.

This crate provides the fundamental building blocks:

• [Request] and [Response] types
• [RequestContext] wrapping asupersync's Cx
• [FromRequest] trait for extractors
• Error types and [IntoResponse] trait

Design Principles

• Zero-copy where possible
• No runtime reflection
• All types support Send + Sync
• Cancel-correct via asupersync integration

Asupersync Integration

This crate uses asupersync as its async runtime foundation, providing:

• Structured concurrency: Request handlers run in regions
• Cancel-correctness: Graceful cancellation via checkpoints
• Budgeted timeouts: Request timeouts via budget exhaustion
• Deterministic testing: Lab runtime for reproducible tests