.Net: Common agent api review feedback 1

[westey-m]

Description

• Moved kernel and kernelarguments to options
• Add multi-message invoke overload
• Seal threads and autocreate on new message
• Restrict usage of deleted threads.
• Added tests for threads logic

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 😄