Add chex as a runtime dependency

[kstonekuan]

Summary

This adds chex==0.1.90 to openpi runtime dependencies.

Why

openpi.models.utils.fsq_tokenizer imports chex at runtime, but chex is not currently declared in pyproject.toml.

In a production inference environment, this caused imports to fail with:

ModuleNotFoundError: No module named 'chex'

Changes

• add chex==0.1.90 to pyproject.toml

Notes

I used 0.1.90 because it is compatible with the current openpi JAX line (jax==0.5.3).

The newer chex>=0.1.91 release requires jax>=0.7.0, so leaving chex unconstrained would risk pulling in an incompatible JAX stack.

[kstonekuan]

Hey @jimmyt857 , struggled with the CI due to the uv lockfile for a bit but this is ready for review now, thanks!

[jimmyt857]

Merge activity

• Apr 15, 3:16 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Apr 15, 3:16 PM UTC: Graphite couldn't merge this PR because it failed for an unknown reason (Fast-forward merges are not supported for forked repositories. Please create a branch in the target repository in order to merge).