feat(vllm-tensorizer): Update `vllm-tensorizer` cloned repository, build with `vllm-flash-attn`, other optimizations

[sangstar]

vllm-tensorizer hasn't had updates since vLLM's formal adoption of tensorizer model loading. An update to build for the most recent commit to vLLM that includes sharded tensorizer support is presented, along with some fixes to successfully build vLLM with recent updates to the source code. These include:

• Building vLLM's wheel from vLLM's source code proper, rather than CoreWeave's vLLM fork (reflecting its official adoption of tensorizer)
• vLLM's adoption of cmake
• Updated xformers version to 0.0.26.post1
• vLLM now formally using their own forked version of flash-attn, which is built here from source