Defining new Jax types with hijax

# Summary Hijax is an experimental JAX feature that allows developers to define custom types beyond standard arrays and pytrees, enabling values to appear as single typed units in JAX computations rather than as flattened array components. These custom types support advanced features like internal invariants, custom derivative rules, vmap batching behavior, and explicit sharding information. The article demonstrates the concept using a quantized array example—arrays stored as int8 values with floating-point scales—and explains how to implement custom types by subclassing HiType and writing VJPHiPrimitive operations.