This PR implements IPv6 blocking functionality to address IP leakage issues where proxied applications inadvertently expose their real IPv6 addresses while IPv4 traffic is properly routed through the SOCKS proxy.

Problem

Users reported that applications like Discord would leak their real IPv6 addresses even when using ProxiFyre to proxy traffic. This occurred because:

1. ProxiFyre only processed IPv4 packets (ETH_P_IP) in the packet filter
2. IPv6 packets (ETH_P_IPV6) were allowed to pass through unprocessed
3. Applications using both IPv4 and IPv6 would proxy IPv4 traffic but expose real IPv6 addresses

This created security issues and caused problems with services like Discord voice channels that rely on consistent IP addressing.

Solution

Added a new blockIPv6 configuration option that, when enabled, drops all IPv6 packets from proxied applications:

{
  "logLevel": "Info",
  "blockIPv6": true,
  "proxies": [...],
  "excludes": [...]
}

Implementation Details

Configuration Layer:

• Added blockIPv6 property to ProxiFyreSettings class with JSON deserialization support
• Fixed constructor-based JSON deserialization issues by converting to property-based classes

C++/CLI Interface:

• Added SetIPv6Blocking(bool enabled) method to Socksifier class
• Implemented method forwarding through the managed/unmanaged boundary

Core Packet Processing:

• Modified packet filter callback in socks_local_router to detect IPv6 packets
• Added atomic flag ipv6_blocking_enabled_ to track blocking state
• IPv6 packets are now dropped when blocking is enabled, preventing IP leaks
• IPv4 packet processing remains unchanged for normal proxy functionality

Filter Management:

• Added helper methods add_ipv6_drop_filters() and remove_ipv6_drop_filters()
• Integrated with existing static filter system for consistent packet handling

Testing

Created validation tests confirming the logic works correctly:

• Without blocking: IPv4=PASS, IPv6=PASS (maintains current behavior)
• With blocking: IPv4=PASS, IPv6=DROP (prevents leaks)

Usage

Users experiencing IPv6 leaks (like Discord voice channel issues) can now add "blockIPv6": true to their configuration. This will:

• Maintain full IPv4 proxy functionality
• Block IPv6 traffic from proxied applications
• Prevent IP address leaks and associated connectivity issues

Example configuration and documentation have been added to guide users.

Fixes #65.

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