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vllm and sglang are now the sub-process engines from #954

Also updated docs on doing vllm and sglang multi-gpu (tensor parallel) and multi-node (pipeline parallel).

Also upgrade the cargo resolver to v3, the default.

New clippy lints:
- `next_back()` instead of `last()` for a double-ended iterator. That avoids walking the whole list.
- ` repeat_n` instead of `repeat.take`. That avoids cloning.
- Doc indenting

Co-authored-by: Ryan Olson <ryanolson@users.noreply.github.com>