Use spans to improve performance in StreamExts.

Also avoid ReadBytes calls that allocate a buffer by either updating the stream position (if not interested in the bytes), by reusing an input buffer (if interested in the bytes), or using a stackalloc buffer to avoid the allocation (for small reads).

OpenRA.Game/FileFormats/ReplayMetadata.cs

@@ -47,7 +47,7 @@ namespace OpenRA.FileFormats
 				throw new NotSupportedException($"Metadata version {version} is not supported");
 
 			// Read game info (max 100K limit as a safeguard against corrupted files)
-			var data = fs.ReadString(Encoding.UTF8, 1024 * 100);
+			var data = fs.ReadLengthPrefixedString(Encoding.UTF8, 1024 * 100);
 			GameInfo = GameInformation.Deserialize(data);
 		}
 
@@ -62,7 +62,7 @@ namespace OpenRA.FileFormats
 			{
 				// Write lobby info data
 				writer.Flush();
-				dataLength += writer.BaseStream.WriteString(Encoding.UTF8, GameInfo.Serialize());
+				dataLength += writer.BaseStream.WriteLengthPrefixedString(Encoding.UTF8, GameInfo.Serialize());
 			}
 
 			// Write total length & end marker