[V0 deprecation] Deprecate V0 Neuron backend

[WoosukKwon]

In vLLM V1, Neuron will be supported as a plugin.

See #21082

[github-actions]

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[gemini-code-assist]

Code Review

This pull request cleanly deprecates and removes the V0 Neuron backend. The changes are comprehensive, covering not only the core implementation files but also associated tests, examples, CI/CD pipeline configurations, and dependency management files. The removal appears to be thorough, with no obvious leftover code or broken references. I found no issues of high or critical severity. The changes align well with the stated objective of moving Neuron support to a plugin for vLLM V1.

[WoosukKwon]

@aarondou Could you please take a look? I'm actually not sure which part will still be needed for your proposal #21082

[aarondou]

Thank you for putting up the changes @WoosukKwon . Will review.

[aarondou]

We will pull the changes down to integrate with our V1 internal implementation to test the changes. The changes to support Neuron on vLLM V1 will be published as PRs at the same time.

[mrinalks]

@WoosukKwon #21082 proposes Neuron as an in-tree implementation (not plugin) on V1 Engine. Please see Change 1 and Change 2 (various options) there. @aarondou let us review the files here and ensure nothing required is actually deleted.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @WoosukKwon.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork