Pyrefly JAX shape stubs

This package is a PEP 561 stub-only distribution. It installs the jax-stubs stub package so Pyrefly can discover shape-aware stubs for the runtime jax package without replacing or shadowing JAX itself. It is versioned in lockstep with Pyrefly and depends on the matching pyrefly-shape-extensions package.

Shape-typed fixture stubs for a subset of JAX. This is a starting point for working with the JAX core team rather than a complete model: it covers array creation, broadcasting arithmetic, matmul, reshape, transpose, the axis/keepdims reductions, and the elementwise activations in jax.nn. Dimensions are modeled and dtypes are not, so adding dtypes later means modeling JAX's own defaults (float32 and int32) rather than copying the NumPy stubs.

Shape rules use the type-level DSL, @type_shape_dsl_function, exclusively. The older @shape_dsl_function and @uses_shape_dsl mechanism is being replaced by it, so nothing here should reach for that: a rule the type-level DSL cannot express yet returns a gradual shape instead. Where a rule is imprecise for that reason, the stub says so at the definition, along with whether a fix is expected.

TENSOR_SHAPES_CONTRIBUTING.md at the repository root covers the workflow, and tensor-shapes/run_tests.py runs the tests. Pyrefly checks the stubs themselves and every test/test_*.py, and those same test files then run against real JAX, so a stub that is self-consistent but wrong still fails.

Anything not listed above is simply absent rather than modeled loosely, so it is reported as a missing attribute rather than inferred gradually.