[ROCm][P/D][MORI][BugFix] Ensure correct api is used when making requests to prefill / decode nodes

[rasmith]

Purpose

This PR fixes the MORI IO KV connector so it uses the correct API when making requests to prefill and decode instances.
Currently, this is broken since the request URL has a /v1/completions suffix which should instead be just /v1. Furthermore, the routes /v1/completions and /v1/chat/completions are not differentiated by the handler, which contributes to the problem. Instead, this PR creates individual routes which then call the main handler function. Finally, the correct URL with the correct API call is used, which fixes the problem.

Test Plan

Please see the Justfile from this PR and the instructions included here. Add this to the Justfile:

eval:
  lm_eval --model local-chat-completions \
    --model_args model={{MODEL}},\
          base_url=http://localhost:10001/v1/chat/completions,\
          num_concurrent=1 \
    --tasks gsm8k \
    --num_fewshot 5 \
    --apply_chat_template \
    --batch_size 1 \
    --gen_kwargs '{"max_tokens": 4096}'

and run:
just -f Justfile.mori eval
where Justfile.mori is the name of the Justfile I chose, but you can pick a different one.

Test Result

The lm_eval session ran successfully and I got the result:

|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value |   |Stderr|
|-----|------:|----------------|-----:|-----------|---|-----:|---|-----:|
|gsm8k|      3|flexible-extract|     5|exact_match|↑  |0.9462|±  |0.0062|
|     |       |strict-match    |     5|exact_match|↑  |0.8893|±  |0.0086|

---

Essential Elements of an Effective PR Description Checklist

• [X ] The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• [ X] The test plan, such as providing test command.
• [ X] The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[mergify]

Documentation preview: https://vllm--39835.org.readthedocs.build/en/39835/

[gemini-code-assist]

Code Review

This pull request refactors the toy proxy server to support both completions and chat completions by modularizing the request handler and dynamically constructing endpoint URLs. It also improves error messaging and updates the ping address in the Moriio connector. A critical syntax error was introduced in moriio_toy_proxy_server.py where a stray closing parenthesis will prevent the code from running.

[rasmith]

@inkcherry Please take a look?

[inkcherry]

LGTM, thanks! @rasmith