fix: Adds ISpanFormattable to Geometry structs (#1231)

* Adds ISpanFormattable to geometry structs and makes ToString() near-zero-allocation.
* Adds IEquatable, and Parsable to Rectangle3D to get it in-line with the other structs.

Closes #1067

Projects/Server.Tests/Tests/Geometry/Point3DTests.cs

@@ -0,0 +1,72 @@
+using System;
+using Xunit;
+
+namespace Server.Tests;
+
+public class Point3DTests
+{
+    [Fact]
+    public void TestPoint3DToString()
+    {
+        const int max = int.MaxValue;
+        const int min = int.MinValue;
+        Assert.Equal("(0, 0, 0)", new Point3D(0, 0, 0).ToString());
+        Assert.Equal("(1, 1, 1)", new Point3D(1, 1, 1).ToString());
+        Assert.Equal($"({max}, {max}, {max})", new Point3D(max, max, max).ToString());
+        Assert.Equal($"({min}, {min}, {min})", new Point3D(min, min, min).ToString());
+    }
+
+    [Fact]
+    public void TestPoint3DTryFormatSucceeds()
+    {
+        const int max = int.MaxValue;
+        const int min = int.MinValue;
+        char[] array = new char[128];
+
+        var p1 = new Point3D(0, 0, 0);
+        Assert.True(p1.TryFormat(array, out var cp1, null, null));
+        Assert.Equal(6 + 3, cp1);
+        Array.Clear(array);
+
+        var p2 = new Point3D(1, 1, 1);
+        Assert.True(p2.TryFormat(array, out var cp2, null, null));
+        Assert.Equal(6 + 3, cp2);
+        Array.Clear(array);
+
+        var p3 = new Point3D(max, max, max);
+        Assert.True(p3.TryFormat(array, out var cp3, null, null));
+        Assert.Equal(6 + 30, cp3);
+        Array.Clear(array);
+
+        var p4 = new Point3D(min, min, min);
+        Assert.True(p4.TryFormat(array, out var cp4, null, null));
+        Assert.Equal(6 + 33, cp4);
+    }
+
+    [Fact]
+    public void TestPoint3DTryFormatFails()
+    {
+        const int max = int.MaxValue;
+        const int min = int.MinValue;
+        char[] array = new char[1];
+
+        var p1 = new Point3D(0, 0, 0);
+        Assert.False(p1.TryFormat(array, out var cp1, null, null));
+        Assert.Equal(0, cp1);
+        Array.Clear(array);
+
+        var p2 = new Point3D(1, 1, 1);
+        Assert.False(p2.TryFormat(array, out var cp2, null, null));
+        Assert.Equal(0, cp2);
+        Array.Clear(array);
+
+        var p3 = new Point3D(max, max, max);
+        Assert.False(p3.TryFormat(array, out var cp3, null, null));
+        Assert.Equal(0, cp3);
+        Array.Clear(array);
+
+        var p4 = new Point3D(min, min, min);
+        Assert.False(p4.TryFormat(array, out var cp4, null, null));
+        Assert.Equal(0, cp4);
+    }
+}