Support basic refactoring from static to sealed

[viceroypenguin]

Fixes #227

[codecov]

Codecov Report

❌ Patch coverage is 86.79245% with 14 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...eFixes/StaticToSealedHandlerRefactoringProvider.cs	87.37%	6 Missing and 7 partials ⚠️
src/Common/SyntaxExtensions.cs	66.66%	0 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ
src/Common/ITypeSymbolExtensions.cs	85.71% <ø> (ø)
src/Common/SyntaxExtensions.cs	66.66% <66.66%> (ø)
...eFixes/StaticToSealedHandlerRefactoringProvider.cs	87.37% <87.37%> (ø)

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[Copilot]

Pull Request Overview

This PR implements a basic refactoring feature that converts static handler classes to sealed instance handlers, supporting issue #227. The refactoring automatically transforms static handlers with dependency injection parameters into sealed classes with primary constructors.

• Adds code refactoring capability to convert static handler classes to sealed instance handlers
• Implements automated parameter transformation from method dependencies to class constructor parameters
• Includes comprehensive test coverage for various refactoring scenarios

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/Immediate.Handlers.Tests/Immediate.Handlers.Tests.csproj	Adds CodeRefactoring.Testing package reference for test infrastructure
tests/Immediate.Handlers.Tests/CodeFixTests/StaticToSealedHandlerRefactoringProviderTests.cs	Comprehensive test suite covering refactoring scenarios including class/method triggers and dependency handling
tests/Immediate.Handlers.Tests/CodeFixTests/HandlerMethodMustExistCodeFixProviderTests.cs	Renames test class for clarity and consistency
tests/Immediate.Handlers.Tests/CodeFixTests/CodeRefactoringTestHelper.cs	Test helper utility for code refactoring test infrastructure
src/Immediate.Handlers.CodeFixes/StaticToSealedHandlerRefactoringProvider.cs	Main refactoring provider implementing static-to-sealed transformation logic
src/Immediate.Handlers.CodeFixes/RefactoringExtensions.cs	Extension methods for refactoring context and document operations
src/Common/SyntaxExtensions.cs	Utility method for CancellationToken type detection
src/Common/ITypeSymbolExtensions.cs	Makes IsCancellationToken method nullable-aware
Directory.Packages.props	Adds CodeRefactoring.Testing package version specification

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