[Test] Add default initialization test

[chhzh123]

Description

This PR adds a test of initialization to make sure the init_weight bypass works in slapo.build. Also, GPU memory usage is measured to ensure init_empty_weights does not introduce extra memory overheads.

Checklist

• PR's title starts with a category (e.g. [Bugfix], [Model], [Tutorial], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented

[comaniac]

LGTM

[comaniac]

Thanks @chhzh123