fix: Add null checks for reflection calls

[thomhurst]

Summary

• Replace null-forgiving operators (!) with explicit null checks and descriptive InvalidOperationException messages in reflection-based method/property lookups
• Affected files:
  • ModuleExecutor.cs: Added null checks for GetMethod, Invoke, GetProperty, and GetValue reflection calls in ExecuteTypedModule method
  • OptionsProvider.cs: Added null check for service resolution and property access via reflection in GetOptions method

Test plan

• Build the solution to verify no compilation errors
• Run unit tests to ensure reflection-based execution still works correctly
• The changes only add validation - if reflection succeeds as before, behavior is unchanged
• If reflection fails, descriptive error messages now help diagnose the issue

Closes #1420

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