Implement tree-like structure for links notation instead of IList<TLinkAddress>

[konard]

Summary

This pull request implements a comprehensive solution for issue #132 by introducing a tree-like representation for links that provides a more hierarchical and flexible approach compared to the traditional flat IList<TLinkAddress> structure.

Key Changes

• ILinkTree Interface: Added ILinkTree<TLinkAddress> interface with tree-like navigation methods
• LinkTree Implementation: Implemented LinkTree<TLinkAddress> struct with full tree functionality
• Enhanced Link Struct: Updated Link<TLinkAddress> struct to implement ILinkTree interface
• Tree-Compatible Extensions: Added tree-compatible extension methods in ILinksExtensions
• Backward Compatibility: Maintained full backward compatibility with existing IList-based APIs
• Conversion Methods: Provided conversion methods between tree and list representations

Features

• Hierarchical Representation: Tree-like structure with parent/child relationships
• Tree Navigation: Methods like GetChild, GetSourceAsTree, GetTargetAsTree
• Seamless Conversion: Implicit conversions between Link, LinkTree, and arrays
• Extended API: New extension methods (SingleOrDefaultTree, AllTrees, FormatTree, etc.)
• Flexible Structure: Support for both flat and hierarchical link structures

Architecture

// New tree interface
public interface ILinkTree<TLinkAddress>
{
    TLinkAddress Index { get; }
    TLinkAddress Source { get; }
    TLinkAddress Target { get; }
    ILinkTree<TLinkAddress>? Parent { get; }
    IEnumerable<ILinkTree<TLinkAddress>> Children { get; }
    // ... navigation and utility methods
}

// Enhanced Link struct now implements both IList and ILinkTree
public struct Link<TLinkAddress> : IEquatable<Link<TLinkAddress>>, 
                                   IReadOnlyList<TLinkAddress>, 
                                   IList<TLinkAddress>, 
                                   ILinkTree<TLinkAddress>
{
    // ... existing functionality plus tree interface implementation
}

Usage Examples

// Traditional approach still works
var link = new Link<ulong>(1, 2, 3);
var array = link.ToArray(); // [1, 2, 3]

// New tree-like approach
ILinkTree<ulong> tree = link;
var index = tree.Index;     // 1
var source = tree.Source;   // 2
var target = tree.Target;   // 3

// Extension methods for tree operations
var result = links.SingleOrDefaultTree(query);
var all = links.AllTrees(restriction);
var formatted = links.FormatTree(tree);

Backward Compatibility

All existing code continues to work without modification:

• IList<TLinkAddress> methods still function as before
• Implicit conversions handle seamless interoperability
• No breaking changes to existing APIs

Testing

• All existing tests pass (21/21 successful)
• Added demonstration script in /experiments/TreeStructureDemo.cs
• Comprehensive compilation with no errors (warnings only)

Test Plan

• Existing test suite passes completely
• Project builds without errors
• Tree interface methods work correctly
• Backward compatibility maintained
• Extension methods function as expected
• Conversion methods work bidirectionally

🤖 Generated with Claude Code

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Resolves #132