feat(network): Add SafePacket, pointer validation, and network tests

Add debug/testing utilities for network packet inspection and first-ever
test coverage for the network monitoring area, as discussed in #2592.

- SafePacket: managed wrapper with bounds checking and lifetime safety
- NetworkPointerValidator: debug utility for pointer address validation
- Make NetworkMonitorWidget.IsFiltered internal static for testability
- Add 49 unit tests covering SafePacket, pointer validation, and opcode
  filter parsing (ranges, exclusions, complex filters)

Dalamud.Test/Game/Network/NetworkPointerValidatorTests.cs

@@ -0,0 +1,90 @@
+using System;
+
+using Dalamud.Game.Network;
+
+using Xunit;
+
+namespace Dalamud.Test.Game.Network;
+
+public class NetworkPointerValidatorTests
+{
+    [Fact]
+    public void NullPointer_ReturnsFalse()
+    {
+        Assert.False(NetworkPointerValidator.IsValidPacketPointer(nint.Zero, 32));
+    }
+
+    [Theory]
+    [InlineData(0x1)]
+    [InlineData(0xFF)]
+    [InlineData(0xFFFF)]
+    public void BelowMinAddress_ReturnsFalse(long address)
+    {
+        Assert.False(NetworkPointerValidator.IsValidPacketPointer((nint)address, 32));
+    }
+
+    [Theory]
+    [InlineData(0x800000000000)]
+    [InlineData(0xFFFFFFFFFFFF)]
+    public void AboveMaxAddress_ReturnsFalse(long address)
+    {
+        Assert.False(NetworkPointerValidator.IsValidPacketPointer((nint)address, 32));
+    }
+
+    [Theory]
+    [InlineData(0)]
+    [InlineData(-1)]
+    [InlineData(-100)]
+    public void NonPositiveSize_ReturnsFalse(int size)
+    {
+        Assert.False(NetworkPointerValidator.IsValidPacketPointer((nint)0x10000, size));
+    }
+
+    [Theory]
+    [InlineData(0x10000, 1)]
+    [InlineData(0x100000, 1024)]
+    [InlineData(0x7FFFFFFFFFFF, 1)]
+    public void ValidPointerAndSize_ReturnsTrue(long address, int size)
+    {
+        Assert.True(NetworkPointerValidator.IsValidPacketPointer((nint)address, size));
+    }
+
+    [Fact]
+    public void SafeRead_InvalidPointer_Throws()
+    {
+        Assert.Throws<ArgumentException>(() =>
+            NetworkPointerValidator.SafeRead<int>(nint.Zero, 0, 32));
+    }
+
+    [Fact]
+    public void SafeRead_NegativeOffset_Throws()
+    {
+        Assert.Throws<ArgumentOutOfRangeException>(() =>
+            NetworkPointerValidator.SafeRead<int>((nint)0x10000, -1, 32));
+    }
+
+    [Fact]
+    public void SafeRead_OffsetExceedsPacket_Throws()
+    {
+        Assert.Throws<ArgumentOutOfRangeException>(() =>
+            NetworkPointerValidator.SafeRead<int>((nint)0x10000, 30, 32));
+    }
+
+    [Fact]
+    public void TrySafeRead_InvalidPointer_ReturnsFalse()
+    {
+        Assert.False(NetworkPointerValidator.TrySafeRead<int>(nint.Zero, 0, 32, out _));
+    }
+
+    [Fact]
+    public void TrySafeRead_NegativeOffset_ReturnsFalse()
+    {
+        Assert.False(NetworkPointerValidator.TrySafeRead<int>((nint)0x10000, -1, 32, out _));
+    }
+
+    [Fact]
+    public void TrySafeRead_OffsetExceedsPacket_ReturnsFalse()
+    {
+        Assert.False(NetworkPointerValidator.TrySafeRead<int>((nint)0x10000, 30, 32, out _));
+    }
+}