Refactor HTTP server

[rmccorm4]

1. Clean up common parsing components of request JSON into helper functions.
   • This will separate some logic between parsing inputs provided in current format ParseJsonTritonIO --> {inputs: {name, datatype, shape}, ...} and accepting json inputs in other formats in future such as {prompt, parameters}.
   • Breaks up a ~400 line EVBufferToInput function into more manageable chunks
2. Return error messages in response body more consistently for most routes. Improved CLI/curl UX, similar to FastAPI and vLLM API server experience.
   • Routes without any handler (not found) will now return 404 instead of 400 at top-level Handler

Error Message UX Details

Before

Query triton routes:

rmccormick@ced35d0-lcedt:~$ curl -w "\n" -X POST localhost:8000/v2

rmccormick@ced35d0-lcedt:~$ curl -w "\n" -X POST localhost:8000/v2/does-not-exist

Responses are blank, so you have to remember to grab the error code:

rmccormick@ced35d0-lcedt:~$ curl -w "%{http_code}\n" -X POST localhost:8000/v2
405
rmccormick@ced35d0-lcedt:~$ curl -w "%{http_code}\n" -X POST localhost:8000/v2/does-not-exist
400

But then you have to go look up what 405 means, and so on

After

Query triton routes:

rmccormick@ced35d0-lcedt:~$ curl -w "\n" -X POST localhost:8000/v2
{"error":"Method Not Allowed"}
rmccormick@ced35d0-lcedt:~$ curl -w "\n" -X POST localhost:8000/v2/does-not-exist
{"error":"Not Found"}

Now it's more immediately obvious what's wrong with our queries.

FastAPI/vLLM for comparison

rmccormick@ced35d0-lcedt:~$ curl -w "\n" -X POST localhost:8080/
{"detail":"Method Not Allowed"}
rmccormick@ced35d0-lcedt:~$ curl -w "\n" -X POST localhost:8080/does-not-exist
{"detail":"Not Found"}

[rmccorm4]

Note for reviewers

I can swap this EVBufferJson block to be with the rest of the helpers and move the HTTPServer Start/Stop and HTTPMetrics server to be down after the helpers with the rest of the server code in a quick follow-up PR.

Doing so in this PR introduces a lot of noise to the amount of actual changes in the diffs.

[rmccorm4]

Note for reviewers

Eventually I think we can provide some mapping between code -> message, but done inline for simplicity. We don't always provide the same error message for 400 (EVHTP_RES_BADREQ) code.

[nnshah1]

Nice work!