Add PrintContents extension method for ILinks interface

[konard]

Summary

Implemented PrintContents extension method for the ILinks<TLinkAddress> interface to provide a configurable way to output the contents of a links database.

Key Features

• ✅ Configurable output handler: Uses Action<string> messageHandler parameter instead of hardcoded Console.WriteLine
• ✅ Empty database handling: Displays "Database is empty." when no links exist
• ✅ Proper formatting: Each link displayed as [linkIndex]: source -> target with zero-padding alignment
• ✅ Generic type support: Works with any TLinkAddress type that implements required constraints

Implementation Details

• Added to ILinksExtensions.cs following existing patterns in the codebase
• Based on the reference implementation from MasterServer.cs#L30-L49
• Uses proper XML documentation following project conventions
• Includes [MethodImpl(MethodImplOptions.AggressiveInlining)] attribute for performance

Example Usage

// Output to console
links.PrintContents(Console.WriteLine);

// Capture to list
var messages = new List<string>();
links.PrintContents(messages.Add);

// Custom handler
links.PrintContents(msg => logger.Info(msg));

Testing

• ✅ All existing tests pass (20/20)
• ✅ Tested with empty database scenario
• ✅ Tested with populated database
• ✅ Verified proper formatting and alignment
• ✅ Added experimental test project for validation

Addresses Issue Requirements

• Resolves the concern about hardcoded Console.WriteLine usage
• Provides the common interface for IO/Logging as requested in Add PrintContents/Output extension method for ILinks interface #150
• Makes the output method customizable for different use cases

Technical Notes

• Method signature: public static void PrintContents<TLinkAddress>(this ILinks<TLinkAddress> links, Action<string> messageHandler)
• Constraints: where TLinkAddress : IUnsignedNumber<TLinkAddress>, IComparisonOperators<TLinkAddress, TLinkAddress, bool>
• Iterates through all links using links.All() method
• Handles null links gracefully with null checks

Fixes #150

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