Add comprehensive duplicate detection test suite with 30 host entries

[Copilot]

This PR adds a comprehensive test suite for the PowerToys Hosts module's duplicate detection functionality. The implementation creates 30 strategically designed host entries that include various types of duplicates to thoroughly test the DuplicateService algorithms.

Test Data Overview

The new DuplicateServiceTest.cs includes:

• 30 total host entries with realistic IP addresses and hostnames
• 6 duplicate groups covering different duplicate scenarios:
  • Exact duplicates (same IP + same hostnames)
  • IPv6 duplicates
  • Loopback address duplicates
  • Case-insensitive duplicates
  • Internal and private network duplicates
• Additional test scenarios including address-only duplicates, host overlaps, and multi-host entries
• 5 unique entries as a control group

Duplicate Detection Scenarios Tested

// Exact duplicates
entries.Add(new Entry(1, "192.168.1.100 example.com"));
entries.Add(new Entry(2, "192.168.1.100 example.com")); // Duplicate

// IPv6 duplicates  
entries.Add(new Entry(11, "2001:db8::1 ipv6test.com"));
entries.Add(new Entry(12, "2001:db8::1 ipv6test.com")); // Duplicate

// Case insensitive duplicates
entries.Add(new Entry(21, "192.168.1.120 CaseSensitive.com"));
entries.Add(new Entry(22, "192.168.1.120 casesensitive.com")); // Duplicate

// Host overlaps
entries.Add(new Entry(9, "192.168.1.104 multi1.com multi2.com"));
entries.Add(new Entry(10, "192.168.1.105 multi2.com multi3.com")); // Overlaps on multi2.com

Key Features

• Comprehensive coverage: Tests IPv4, IPv6, loopback, private networks, and mixed-case scenarios
• Realistic data: Uses valid IP address ranges and realistic hostname patterns
• Well-documented: Extensive XML documentation explains each test scenario
• Validated structure: Includes validation logic to ensure test data integrity
• Background processing aware: Accounts for the asynchronous nature of DuplicateService

The test suite serves as both validation for the duplicate detection functionality and documentation for how the PowerToys Hosts module handles various duplicate scenarios in real-world host files.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• i1qvsblobprodcus353.vsblob.vsassets.io
  • Triggering command: dotnet build src/modules/Hosts/Hosts.Tests/HostsEditor.UnitTests.csproj (dns block)
  • Triggering command: dotnet build src/modules/Hosts/HostsUILib/HostsUILib.csproj --no-restore (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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