Install tpu requirements by default in pypi

[SurbhiJainUSC]

Description

Adds TPU dependencies as default dependencies to pyproject.toml. This ensures that when we release new version of MaxText, then both pip install maxtext and pip install maxtext[tpu] will install TPU-specific dependencies, and pip install maxtext[gpu] will install GPU-specific dependencies.

Tests

Build wheel file, installed MaxText and dependencies using wheel file & tested training

Checklist

Before submitting this PR, please make sure (put X in square brackets):

• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.