parse: 'arrayBuffer' produces empty content in OpenAPI spec

[pae-blue]

When using parse: 'arrayBuffer' with a body schema, the generated OpenAPI spec has an empty content object in requestBody:

{
  "requestBody": {
    "description": "Audio file as binary data",
    "content": {},
    "required": true
  }
}

This causes OpenAPI-to-TypeScript generators to infer the body type as undefined.

The switch in src/openapi.ts of @elysiajs/openapi handles text, urlencoded, json, and formdata, but not arrayBuffer. Same root cause as #1720 (which covers parse: 'none').

Reproduction:

const app = new Elysia().post('/upload', ({ body }) => 'ok', {
  parse: 'arrayBuffer',
  body: t.Any({ description: 'Binary file data' }),
})

A possible fix would be adding arrayBuffer as a case mapping to application/octet-stream, and/or a fallback for any unmatched parse mode so this can't recur.