chore(misc): make tests and starter faster (#3042)

A bunch of miscellaneous cleanup focusing on tests, but ended up
speeding up starter distro substantially.

- Pulled llama stack client init for tests into `pytest_sessionstart` so
it does not clobber output
- Profiling of that told me where we were doing lots of heavy imports
for starter, so lazied them
- starter now starts 20seconds+ faster on my Mac
- A few other smallish refactors for `compat_client`

scripts/provider_codegen.py

@@ -10,6 +10,7 @@ import sys
 from pathlib import Path
 from typing import Any
 
+from pydantic_core import PydanticUndefined
 from rich.progress import Progress, SpinnerColumn, TextColumn
 
 from llama_stack.core.distribution import get_provider_registry
@@ -59,6 +60,8 @@ def get_config_class_info(config_class_path: str) -> dict[str, Any]:
         if hasattr(config_class, "model_fields"):
             for field_name, field in config_class.model_fields.items():
                 field_type = str(field.annotation) if field.annotation else "Any"
+
+                # this string replace is ridiculous
                 field_type = field_type.replace("typing.", "").replace("Optional[", "").replace("]", "")
                 field_type = field_type.replace("Annotated[", "").replace("FieldInfo(", "").replace(")", "")
                 field_type = field_type.replace("llama_stack.apis.inference.inference.", "")
@@ -77,7 +80,7 @@ def get_config_class_info(config_class_path: str) -> dict[str, Any]:
                                 default_value = f"~/.llama/{path_part}"
                     except Exception:
                         default_value = ""
-                elif field.default is None:
+                elif field.default is None or field.default is PydanticUndefined:
                     default_value = ""
 
                 field_info = {
@@ -255,7 +258,7 @@ def process_provider_registry(progress, change_tracker: ChangedPathTracker) -> N
             change_tracker.add_paths(doc_output_dir)
 
             index_content = []
-            index_content.append(f"# {api_name.title()} \n")
+            index_content.append(f"# {api_name.title()}\n")
             index_content.append("## Overview\n")
 
             index_content.append(