Find CustomHandler or KeySelector methods if they are defined in base types

[Dreamescaper]

No description provided.

[Copilot]

Pull Request Overview

Enhances the source generator to find CustomHandler and KeySelector methods from base types, not just the containing type directly. This allows inheritance of these methods from parent classes.

• Replaces direct member searches with a new GetMethod extension method that traverses inheritance hierarchy
• Adds accessibility and static context validation using SemanticModel.IsAccessible
• Updates method signature to include SemanticModel parameter for accessibility checks

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
ServiceScan.SourceGenerator/Model/AttributeModel.cs	Updates Create method to use new GetMethod extension and pass SemanticModel
ServiceScan.SourceGenerator/Extensions/TypeSymbolExtensions.cs	Adds new extension method that searches inheritance hierarchy with accessibility checks
ServiceScan.SourceGenerator/DependencyInjectionGenerator.ParseMethodModel.cs	Updates method calls to use new GetMethod extension and refactors loop
ServiceScan.SourceGenerator.Tests/CustomHandlerTests.cs	Adds test case verifying inheritance functionality works correctly

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