Add IUtf8SpanFormattable template

src/StructId.FunctionalTests/Functional.cs

@@ -1,4 +1,5 @@
 using System.Diagnostics.CodeAnalysis;
+using System.Text;
 using Dapper;
 using Microsoft.Data.Sqlite;
 using Microsoft.EntityFrameworkCore;
@@ -140,6 +141,26 @@ public void StringIdDoesNotImplementISpanFormattable()
         Assert.IsNotAssignableFrom<ISpanFormattable>(WalletId.New("foo"));
     }
 
+    [Fact]
+    public void GuidImplementUtf8SpanFormattable()
+    {
+        var id = ProductId.New();
+
+        Assert.IsAssignableFrom<IUtf8SpanFormattable>(id);
+
+        Span<byte> utf8Destination = new byte[36]; // Typical GUID length in string form
+
+        if (id.TryFormat(utf8Destination, out int bytesWritten, default, null))
+        {
+            var guid = new Guid(Encoding.UTF8.GetString(utf8Destination.Slice(0, bytesWritten)));
+            Assert.Equal(id.Value, guid);
+        }
+        else
+        {
+            Assert.Fail("TryFormat failed");
+        }
+    }
+
     public class Context : DbContext
     {
         public Context(DbContextOptions<Context> options) : base(options) { }

src/StructId/Templates/Utf8SpanFormattable.cs

@@ -0,0 +1,12 @@
+// <auto-generated />
+#nullable enable
+
+using System;
+using StructId;
+
+[TStructId]
+file partial record struct Utf8SpanFormattable(IUtf8SpanFormattable Value) : IUtf8SpanFormattable
+{
+    public bool TryFormat(Span<byte> utf8Destination, out int bytesWritten, ReadOnlySpan<char> format, IFormatProvider? provider) 
+        => Value.TryFormat(utf8Destination, out bytesWritten, format, provider);
+}