[BUG] remove flax==0.12.4 constraint for sglang

[aolemila]

Refer to #1205

Expected Behavior

Actual Behavior

Steps to Reproduce the Problem

Environment

• OS: [e.g., Ubuntu, etc.]
• Project Version: [e.g., 0.0.1]

Checklist

• I have searched the existing issues for a similar bug report.
• I have provided all the required information in the "Environment" section.
• I have provided a minimal, reproducible example.

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