py : type-check all Python scripts with Pyright (#8341)

* py : type-check all Python scripts with Pyright

* server-tests : use trailing slash in openai base_url

* server-tests : add more type annotations

* server-tests : strip "chat" from base_url in oai_chat_completions

* server-tests : model metadata is a dict

* ci : disable pip cache in type-check workflow

The cache is not shared between branches, and it's 250MB in size,
so it would become quite a big part of the 10GB cache limit of the repo.

* py : fix new type errors from master branch

* tests : fix test-tokenizer-random.py

Apparently, gcc applies optimisations even when pre-processing,
which confuses pycparser.

* ci : only show warnings and errors in python type-check

The "information" level otherwise has entries
from 'examples/pydantic_models_to_grammar.py',
which could be confusing for someone trying to figure out what failed,
considering that these messages can safely be ignored
even though they look like errors.

examples/pydantic_models_to_grammar_examples.py

@@ -1,6 +1,7 @@
 # Function calling example using pydantic models.
+from __future__ import annotations
+
 import datetime
-import importlib
 import json
 from enum import Enum
 from typing import Optional, Union
@@ -215,9 +216,9 @@ for call in json_data:
     if call["function"] == "Calculator":
         print(Calculator(**call["params"]).run())
     elif call["function"] == "get_current_datetime":
-        print(current_datetime_model(**call["params"]).run())
+        print(current_datetime_model(**call["params"]).run())  # pyright: ignore[reportAttributeAccessIssue]
     elif call["function"] == "get_current_weather":
-        print(current_weather_tool_model(**call["params"]).run())
+        print(current_weather_tool_model(**call["params"]).run())  # pyright: ignore[reportAttributeAccessIssue]
 # Should output something like this:
 # 2024-01-14 13:36:06
 # {"location": "London", "temperature": "42", "unit": "celsius"}