fix: Eliminates string allocations while writing gump packets (#1017)

* Introduces `RawInterpolatedStringHandler` which is exactly the same as `DefaultInterpolatedStringHandler` except it _unsafely exposes_ it's `ReadOnlySpan<char>` buffer. This is useful for writing the string's data without actually building the string.
* Uses this new string interpolation handler in `SpanWriter` to eliminate intermediate strings built. This is immensely useful in eliminating string allocations in writing Gump packets.

Projects/Server/Buffers/PooledArraySpanFormattable.cs

@@ -15,7 +15,6 @@
 
 #nullable enable
 using System;
-using System.Buffers;
 
 namespace Server.Buffers;
 
@@ -64,7 +63,7 @@ public struct PooledArraySpanFormattable : ISpanFormattable, IDisposable
     {
         if (_arrayToReturnToPool != null)
         {
-            ArrayPool<char>.Shared.Return(_arrayToReturnToPool);
+            STArrayPool<char>.Shared.Return(_arrayToReturnToPool);
             _arrayToReturnToPool = null;
         }
     }