* (GH-4617) Remove unnecessary using directives&enforce IDE0005

- Add IDE0005 severity as error in .editorconfig
- Remove unused using directives across Cake.Common, Cake.Core, Cake.Frosting, and Cake.NuGet
- Enable EnforceCodeStyleInBuild in Shared.msbuild
- Clean up imports in 50+ files to improve code quality and reduce compilation warnings
- fixes #4617

* Add XML documentation to Cake.Testing.Xunit

- Add GenerateDocumentationFile to project files
- Add comprehensive XML documentation for all public types and members
- Resolve CS1591 warnings for missing XML comments
- Document AssertEx methods, platform attributes, and TestRuntime enum

* Fix StyleCop SA1514 error and disable code style enforcement for test projects

- Add blank line before CoreClr documentation in TestRuntime.cs
- Disable EnforceCodeStyleInBuild for Cake test projects

* feat: Add comprehensive XML documentation and enable documentation generation

- Enable GenerateDocumentationFile in Cake.csproj to generate XML docs
- Add XML documentation comments for all public types and members:
  * DefaultCommand and DefaultCommandSettings classes
  * BootstrapFeature, BuildFeature, and related settings classes
  * All infrastructure classes in Composition and Scripting namespaces
  * Program class and core components
- Remove unnecessary using directives (System.Linq, System.IO, Spectre.Console.Cli)
- Fix code formatting and trailing whitespace issues
- Resolve CS1591 XML documentation warnings for public API

* fix: Exclude example projects from code style enforcement

- Add IsPackable=false to Cake.Frosting.Example project
- Update EnforceCodeStyleInBuild condition to exclude non-packable projects
- Prevents code style enforcement on example/demo projects that don't need strict compliance

* feat: Enable XML documentation generation for test tasks project

- Add GenerateDocumentationFile=true to Cake.Frosting.Tests.Tasks project
- Suppress CS1591 warnings for missing XML documentation
- Maintains documentation generation while allowing flexibility for test code

* fix: Move code style enforcement to Release configuration only

- Remove EnforceCodeStyleInBuild from global configuration
- Add EnforceCodeStyleInBuild to Release-only PropertyGroup with enhanced conditions
- Ensures code style enforcement only applies to Release builds for packable, non-test projects
- Improves build performance for Debug/development builds

* fix: Mark Cake.Frosting.Tests as test project

- Add IsCakeTestProject=true to Cake.Frosting.Tests project
- Ensures test project is excluded from code style enforcement in Release builds
- Aligns with existing test project configuration pattern