Python: mypy coverage enhancement

[eavanvalkenburg]

Motivation and Context

extend mypy coverage for prompt_templates, template_engine and some other smaller folders.

still todo: connectors, memory and planner folders.

Description

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 3.10 Test Coverage Report •

File	Stmts	Miss	Cover	Missing
semantic_kernel
kernel.py	93	38	59%	124, 131–140, 178–186, 257–293
semantic_kernel/core_plugins
conversation_summary_plugin.py	16	8	50%	37–38, 64–73
web_search_engine_plugin.py	9	2	78%	28, 38
semantic_kernel/core_plugins/sessions_python_tool
sessions_python_plugin.py	102	14	86%	59–61, 81, 84, 89–95, 134, 185, 189
semantic_kernel/functions
kernel_function_from_prompt.py	161	7	96%	159–160, 181, 201, 226, 247, 327
semantic_kernel/planners/function_calling_stepwise_planner
function_calling_stepwise_planner.py	115	43	63%	132–222, 257–262
semantic_kernel/planners/sequential_planner
sequential_planner.py	64	6	91%	69, 73, 107, 123, 132–133
semantic_kernel/template_engine/blocks
named_arg_block.py	43	1	98%	98
TOTAL	6076	780	87%

Python 3.10 Unit Test Overview

Tests	Skipped	Failures	Errors	Time
1402	1 💤	0 ❌	0 🔥	20.352s ⏱️