Basic flashinfer 0.2 support (#2862)
* Basic flashinfer 0.2 support
This change does not use any of the new features yet, but makes
some small compatibility changes.
* Update to flashinfer 0.2.0.post1
* flashinfer: remove `contiguous` calls
* Fix flashinfer install
* flashinfer: fixup kv cache dtype
* Fix some annoying perturbations
* More output changes
