Python: Fix non-string KernelArguments being converted to strings in prompt template function calls

[moonbox3]

Motivation and Context

Fixes #13199 - Non-string kernel arguments are now preserved when passed to functions in prompt templates. Adds unit 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
template_engine/blocks
code_block.py	84	1	98%	119
var_block.py	41	1	97%	98
TOTAL	27309	4561	83%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3763	23 💤	0 ❌	0 🔥	1m 39s ⏱️