feat: make telemetry attributes be dict[str,PrimitiveType] (#1055)

# What does this PR do?
Make attributes in telemetry be only primitive types and avoid arbitrary
nesting.

## Test Plan
```
 LLAMA_STACK_DISABLE_VERSION_CHECK=true llama stack run ~/.llama/distributions/fireworks/fireworks-run.yaml
LLAMA_STACK_BASE_URL=http://localhost:8321 pytest -v tests/client-sdk/agents/test_agents.py  -k "test_builtin_tool_web_search"
# Verified that attributes still show up correclty in jaeger
```

llama_stack/apis/telemetry/telemetry.py

@@ -17,6 +17,7 @@ from typing import (
     runtime_checkable,
 )
 
+from llama_models.llama3.api.datatypes import Primitive
 from llama_models.schema_utils import json_schema_type, register_schema, webmethod
 from pydantic import BaseModel, Field
 from typing_extensions import Annotated
@@ -76,7 +77,7 @@ class EventCommon(BaseModel):
     trace_id: str
     span_id: str
     timestamp: datetime
-    attributes: Optional[Dict[str, Any]] = Field(default_factory=dict)
+    attributes: Optional[Dict[str, Primitive]] = Field(default_factory=dict)
 
 
 @json_schema_type

llama_stack/providers/utils/telemetry/trace_protocol.py

@@ -9,12 +9,13 @@ import inspect
 from functools import wraps
 from typing import Any, AsyncGenerator, Callable, Type, TypeVar
 
+from llama_models.llama3.api.datatypes import Primitive
 from pydantic import BaseModel
 
 T = TypeVar("T")
 
 
-def serialize_value(value: Any) -> Any:
+def serialize_value(value: Any) -> Primitive:
     """Serialize a single value into JSON-compatible format."""
     if value is None:
         return ""
@@ -24,10 +25,6 @@ def serialize_value(value: Any) -> Any:
         return value._name_
     elif isinstance(value, BaseModel):
         return value.model_dump_json()
-    elif isinstance(value, (list, tuple, set)):
-        return [serialize_value(item) for item in value]
-    elif isinstance(value, dict):
-        return {str(k): serialize_value(v) for k, v in value.items()}
     else:
         return str(value)