#sdy Add JAX backwards compatibility test.
This tests saving a module with one set of axis names, but loading it with another set of axis names.
This does also test the custom calls:
- `@Sharding`
- `@xla.sdy.GlobalToLocalShape`
- `@xla.sdy.LocalToGlobalShape`
But note that there are a bunch of other custom calls that will be tested in the Shardy and XLA codebases. The way the testing utils is tested here doesn't allow me to set `out_shardings` for example. So JAX can rely on the existence of those tests as stability guarantees just like for StableHLO.
PiperOrigin-RevId: 732893432
