Python: mypy coverage for the smaller folders

[eavanvalkenburg]

Motivation and Context

Extend mypy coverage for three of the smaller folders still to go

Description

Contribution Checklist

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

[markwallace-microsoft]

Python 3.10 Test Coverage Report •

File	Stmts	Miss	Cover	Missing
semantic_kernel
kernel.py	267	56	79%	118, 120, 184, 189–198, 203–212, 242, 252–259, 331–367, 437–438, 665, 686–688, 724, 726, 736
semantic_kernel/reliability
pass_through_without_retry.py	13	5	62%	26–30
semantic_kernel/services
ai_service_client_base.py	20	1	95%	10
ai_service_selector.py	24	2	92%	42, 51
semantic_kernel/text
text_chunker.py	113	4	96%	208, 231, 248, 308
TOTAL	6111	1086	82%

Python 3.10 Unit Test Overview

Tests	Skipped	Failures	Errors	Time
1291	1 :zzz:	0 :x:	0 :fire:	11.698s :stopwatch:

[eavanvalkenburg]

merged into #6250