[pallas] Does not support initialising complex values

[PhilipVinc]

Description

See #30043

System info (python version, jaxlib version, accelerator, etc.)

jax 0.6.3

[justinjfu]

Hi, do you have an example of a kernel you are trying to write (or even just pseudocode)?

We've never considered complex numbers in Pallas and I'm not sure if it's a good idea to support them at the Pallas level since the compiler backends do not explicitly support complex types.

[PhilipVinc]

it was some normal jax code, but I lost the reproducer.
It was arising inside of a custom_vjp.
If I'll ever hit this bug again I'll let you know.