Op
A single registered operation in the warp op registry.
The contract is deliberately type-erased: arguments and results are opaque ByteArrays. This keeps OpRegistry serialization-friendly and target-agnostic — typed wrappers (encoding/decoding the ByteArray to/from a domain type) can be layered on top by callers.
An Op may suspend (e.g. to delegate CPU-bound work to a background dispatcher or perform I/O), but must not rely on any external mutable state that outlives the call.