Python: bug fixes from graphrag insights

[eavanvalkenburg]

Motivation and Context

Based on insights from the graphrag team, several bug fixes related to data and model validators.

Description

For all cases of model_validator in before mode, there is no guarantee that the data passed is a dict,
especially when a model is used as a field in another model, then a string is passed to the before validator.
So in those cases we check before doing logic, otherwise just pass it on and let Pydantic handle the invalid data.

Some small logic fixes in the vector store model decorator:

• updated docstring with the right exceptions
• additional checks on attributes
• additional checks on VectorFields with tests

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/agents/group_chat
broadcast_queue.py	74	1	99%	37
semantic_kernel/connectors/ai/open_ai/prompt_execution_settings
open_ai_prompt_execution_settings.py	101	2	98%	127, 141
semantic_kernel/data/text_search
text_search.py	75	2	97%	269–271
utils.py	30	2	93%	57–58
semantic_kernel/functions
kernel_function_from_prompt.py	155	7	95%	168–169, 183, 204, 222, 242, 325
semantic_kernel/processes/local_runtime
local_step.py	164	100	39%	62, 72, 81–169, 173, 177, 181–182, 187–249, 253–256, 260–263, 267–276, 282–285, 289–291
TOTAL	16749	1782	89%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3012	4 💤	0 ❌	0 🔥	1m 27s ⏱️