Add LUKVPress 🤖🤖🤖

[molanyu]

PR description

This PR adds a new KV cache compression method, LUKV:
arxiv: https://arxiv.org/abs/2602.08585
code: https://github.com/baidu-baige/LU-KV

Checklist

Before submitting a PR, please make sure:

• Tests are working (make test)

• Code is formatted correctly (make style, on errors try fix with make format)

• Copyright header is included

• All commits are signed-off using git commit -s

• (new press) mypress_press.py is in the presses directory

• (new press) MyPress is in __init__.py

• (new press) README.md is updated with a 1 liner about the new press in the Available presses section

• (new press) New press is in the default_presses list in tests/default_presses.py

• (new press) A docstring is provided that follows the same structure as the existing ones

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