chore: refactor (chat)completions endpoints to use shared params struct (#3761)

# What does this PR do?

Converts openai(_chat)_completions params to pydantic BaseModel to
reduce code duplication across all providers.

## Test Plan
CI









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[//]: # (BEGIN SAPLING FOOTER)
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[ReviewStack](https://reviewstack.dev/llamastack/llama-stack/pull/3761).
* #3777
* __->__ #3761

docs/openapi_generator/pyopenapi/utility.py

@@ -8,10 +8,11 @@ import json
 import typing
 import inspect
 from pathlib import Path
-from typing import TextIO
-from typing import Any, List, Optional, Union, get_type_hints, get_origin, get_args
+from typing import Any, List, Optional, TextIO, Union, get_type_hints, get_origin, get_args
 
+from pydantic import BaseModel
 from llama_stack.strong_typing.schema import object_to_json, StrictJsonType
+from llama_stack.strong_typing.inspection import is_unwrapped_body_param
 from llama_stack.core.resolver import api_protocol_map
 
 from .generator import Generator
@@ -205,6 +206,14 @@ def _validate_has_return_in_docstring(method) -> str | None:
 def _validate_has_params_in_docstring(method) -> str | None:
     source = inspect.getsource(method)
     sig = inspect.signature(method)
+
+    params_list = [p for p in sig.parameters.values() if p.name != "self"]
+    if len(params_list) == 1:
+        param = params_list[0]
+        param_type = param.annotation
+        if is_unwrapped_body_param(param_type):
+            return
+
     # Only check if the method has more than one parameter
     if len(sig.parameters) > 1 and ":param" not in source:
         return "does not have a ':param' in its docstring"