This PR introduces the new Cake.Issues.Build library to provide a cleaner separation between pull request systems and build servers, addressing the confusing naming issue where build server addins were using Cake.Issues.PullRequests.

What's New

New Cake.Issues.Build Library

• Focused API: Contains only functionality relevant to build servers without pull request-specific capabilities
• Simplified Settings: Includes MaxIssuesToPost, MaxIssuesToPostForEachIssueProvider, ProviderIssueLimits (as Dictionary<string, int>), and IssueFilters
• Base Class: BaseBuildServerSystem provides foundation for build server implementations without capabilities system
• Complete Aliases: ReportIssuesToBuildServer methods for all usage scenarios

Shared Infrastructure

• IssueFiltering: Shared source project containing common issue filtering logic that both pull request and build server systems can use
• Reusable Components: IHasIssueFiltering interface and BasicIssueFilterer class enable code sharing

NuGet Package Support

• Full package specifications for both Cake .NET Tool (Cake.Issues.Build) and Cake Frosting (Cake.Frosting.Issues.Build)
• Proper dependency management and namespace imports via targets files

Usage Example

// Report issues to a custom build server
var settings = new ReportIssuesToBuildServerSettings(@"C:\repo")
{
    MaxIssuesToPost = 10
};

var result = ReportIssuesToBuildServer(
    issues,
    new MyBuildServerSystem(Context.Log),
    settings);

Context.Information($"{result.PostedIssues.Count()} issues reported");

Backward Compatibility

All existing functionality in Cake.Issues.PullRequests continues to work unchanged. The shared issue filtering logic is now used by both libraries, ensuring consistent behavior while eliminating code duplication.

Testing

• 10 unit tests covering settings, base classes, and integration scenarios
• 318 existing tests continue to pass, ensuring no regressions
• Integration test demonstrates complete workflow with custom build server implementation

Future build server implementations should use the new Cake.Issues.Build library, while existing implementations can be migrated gradually without breaking changes.

Fixes #1237.