Python: Exclude certain fields from KernelFunction model dump

[moonbox3]

Motivation and Context

When trying to do a model dump for KernelFunction models, they are failing with a message related to:

pydantic_core._pydantic_core.PydanticSerializationError: Unable to serialize unknown type: <class 'type'>

There are some class-level attributes that cannot be properly serialized.

Description

Exclude dumping certain model attributes from the model dump, which allows the main KernelFunction metadata and its underlying parameters to be serialized.

• Closes Python: Bug: KernelFunction model_dump(mode="json") fails #11078
• Adds unit tests to ensure we have coverage and can dump Pydantic models.

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/functions
kernel_function_from_method.py	96	1	99%	153
TOTAL	20883	2332	89%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3334	5 💤	0 ❌	0 🔥	1m 40s ⏱️