test(network): add Moq mocking library with networking test examples

[Copilot]

Added Moq (most popular .NET mocking library) to the test suite and created example tests demonstrating its usage with networking interfaces.

Changes

• Added Moq v4.20.72 package reference to Void.Tests.csproj
• Created NetworkTests.cs with 13 example tests covering:
  • INetworkChannel: async message operations, pause/resume controls, lifecycle
  • INetworkStream: async I/O with buffer management
• Added project reference to Void.Proxy.Plugins.Common for network testing

Example Usage

[Fact]
public async Task NetworkChannel_ReadMessageAsync_WhenMessageAvailable_ReturnsMessage()
{
    var mockChannel = new Mock<INetworkChannel>();
    var mockMessage = new Mock<INetworkMessage>();

    mockChannel.Setup(c => c.ReadMessageAsync(It.IsAny<CancellationToken>()))
        .ReturnsAsync(mockMessage.Object);

    var message = await mockChannel.Object.ReadMessageAsync();

    Assert.NotNull(message);
    mockChannel.Verify(c => c.ReadMessageAsync(It.IsAny<CancellationToken>()), Times.Once);
}

Tests demonstrate Setup/Verify patterns, async testing, and callback capture for validation.

Original prompt

Add most popular mocking library and add few example networking tests with it

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