Python: Fix issues of Google AI/Vertex AI on handling classes in kernel functions

[TaoChenOSU]

Motivation and Context

Address #8110

Description

1. Bug fix: parse function result to string
2. Integration tests added against complex type in function calling.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[markwallace-microsoft]

Python Test Coverage Report

File	Stmts	Miss	Cover	Missing
semantic_kernel
kernel.py	199	47	76%	148, 159, 163, 313–316, 423, 437–480
semantic_kernel/agents/channels
open_ai_assistant_channel.py	49	1	98%	42
semantic_kernel/agents/group_chat
agent_chat.py	116	1	99%	91
agent_group_chat.py	67	2	97%	113, 135
broadcast_queue.py	72	1	99%	35
semantic_kernel/agents/open_ai
assistant_content_generation.py	68	2	97%	81–82
open_ai_assistant_base.py	361	3	99%	243, 321–322
semantic_kernel/connectors/ai
chat_completion_client_base.py	104	3	97%	364, 374, 384
semantic_kernel/connectors/ai/azure_ai_inference/services
azure_ai_inference_chat_completion.py	107	3	97%	133, 153, 175
semantic_kernel/connectors/ai/embeddings
embedding_generator_base.py	8	1	88%	50
semantic_kernel/connectors/ai/google
shared_utils.py	39	6	85%	57–59, 97, 118–121
semantic_kernel/connectors/ai/google/google_ai/services
google_ai_chat_completion.py	117	4	97%	124, 149, 172, 174
google_ai_text_completion.py	61	2	97%	95, 117
utils.py	65	3	95%	140, 160–165
semantic_kernel/connectors/ai/google/vertex_ai/services
utils.py	66	3	95%	141, 161–166
vertex_ai_chat_completion.py	117	4	97%	117, 142, 165, 167
vertex_ai_text_completion.py	60	2	97%	91, 111
semantic_kernel/connectors/ai/hugging_face/services
hf_text_completion.py	59	3	95%	100, 109, 123
hf_text_embedding.py	32	5	84%	79–83
semantic_kernel/connectors/ai/ollama/services
ollama_chat_completion.py	51	2	96%	93, 127
ollama_text_completion.py	48	2	96%	88, 115
semantic_kernel/connectors/ai/open_ai/services
open_ai_chat_completion_base.py	117	2	98%	114, 257
semantic_kernel/connectors/memory/azure_ai_search
azure_ai_search_collection.py	87	2	98%	150, 152
semantic_kernel/connectors/memory/redis
redis_collection.py	160	2	99%	146, 316
utils.py	45	11	76%	145–146, 164, 166, 173–188
semantic_kernel/connectors/openapi_plugin
openapi_manager.py	58	2	97%	110–111
openapi_parser.py	88	1	99%	127
openapi_runner.py	105	2	98%	181–182
semantic_kernel/connectors/openapi_plugin/models
rest_api_operation.py	129	1	99%	242
semantic_kernel/contents
function_call_content.py	97	1	99%	201
semantic_kernel/data
vector_store_record_collection.py	249	19	92%	410, 470–474, 482–486, 526–529, 536–539
vector_store_record_utils.py	26	2	92%	50, 52
semantic_kernel/functions
kernel_function_decorator.py	98	1	99%	102
kernel_function_from_method.py	96	1	99%	153
kernel_function_from_prompt.py	154	7	95%	165–166, 180, 201, 219, 239, 322
kernel_function_log_messages.py	36	6	83%	37–43
kernel_plugin.py	187	2	99%	472, 475
semantic_kernel/planners
plan.py	234	45	81%	54, 163–165, 197, 214–227, 264, 269, 277–278, 288–291, 308, 313, 329, 332–337, 355, 360, 363, 365, 372, 386–388, 393–397
semantic_kernel/planners/function_calling_stepwise_planner
function_calling_stepwise_planner.py	116	4	97%	145, 189–190, 198
semantic_kernel/planners/sequential_planner
sequential_planner.py	64	6	91%	71, 75, 109, 125, 134–135
sequential_planner_extensions.py	50	9	82%	31–32, 56, 110–124
sequential_planner_parser.py	77	12	84%	66–74, 93, 117–120
semantic_kernel/schema
kernel_json_schema_builder.py	119	5	96%	50, 84, 206, 210–211
semantic_kernel/template_engine/blocks
code_block.py	77	1	99%	119
named_arg_block.py	43	1	98%	98
semantic_kernel/utils/telemetry
user_agent.py	16	2	88%	18–19
semantic_kernel/utils/telemetry/model_diagnostics
decorators.py	105	2	98%	210, 214
TOTAL	10742	249	98%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2383	1 💤	0 ❌	0 🔥	52.381s ⏱️