feat: Added AppendSpan

Author: bCamba

src/LinkDotNet.StringBuilder/ValueStringBuilder.Append.cs

@@ -136,6 +136,19 @@ public void AppendLine(scoped ReadOnlySpan<char> str)
         Append(string.Concat(str, Environment.NewLine));
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public Span<char> AppendSpan(int length)
+    {
+        int origPos = bufferPosition;
+        if (origPos > buffer.Length - length)
+        {
+            Grow(length);
+        }
+
+        bufferPosition = origPos + length;
+        return buffer.Slice(origPos, length);
+    }
+
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private void AppendSpanFormattable<T>(T value, ReadOnlySpan<char> format = default, int bufferSize = 36)
         where T : ISpanFormattable

tests/LinkDotNet.StringBuilder.UnitTests/ValueStringBuilder.Append.Tests.cs

@@ -47,6 +47,18 @@ public void ShouldAppendLine()
         stringBuilder.ToString().Should().Contain("Hello").And.Contain(Environment.NewLine);
     }
 
+    [Fact]
+    public void ShouldAppendSpan()
+    {
+        using var stringBuilder = new ValueStringBuilder();
+
+        var returned = stringBuilder.AppendSpan(2);
+
+        stringBuilder.Length.Should().Be(2);
+
+        stringBuilder.ToString().Should().Be(returned.ToString());
+    }
+
     [Fact]
     public void ShouldOnlyAddNewline()
     {