fix: Filter out open generics when used with CustomHandler

[Dreamescaper]

No description provided.

[Copilot]

Pull Request Overview

This PR aims to prevent generation of registrations for generic (open) implementation types when a CustomHandler is used, and to improve clarity by using named arguments in service registration construction.

• Add filtering to skip generic types when a CustomHandler is specified.
• Use named arguments for ResolveImplementation and IsOpenGeneric to improve readability.
• Add a unit test and update the playground to demonstrate decorator-based custom handling.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
ServiceScan.SourceGenerator/DependencyInjectionGenerator.FindServicesToRegister.cs	Switch to named arguments for ResolveImplementation/IsOpenGeneric, clarifying intent in service registration construction.
ServiceScan.SourceGenerator/DependencyInjectionGenerator.FilterTypes.cs	Add filter to skip generic types when a CustomHandler is present.
ServiceScan.SourceGenerator.Tests/CustomHandlerTests.cs	Add test to validate decorated handler generation for non-generic implementations.
ServiceScan.SourceGenerator.Playground/ServiceCollectionExtensions.cs	Update playground to show CustomHandler with decorator pattern.

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}