Document position advancement in MemoryStream.WriteByte

Added documentation to clarify that WriteByte advances the tream's
  position by one byte on success, matching the documentation style of the Write method. This addresses confusion about position behavior.

Author: oii-nasif

xml/System.IO/MemoryStream.xml

@@ -2817,6 +2817,8 @@ The underlying buffer will not be exposed if the current `MemoryStream` instance
 ## Remarks
  This method overrides <xref:System.IO.Stream.WriteByte%2A>.
 
+ If the write operation is successful, the current position within the stream advances by one byte. If an exception occurs, the current position within the stream is unchanged.
+            
  Except for a `MemoryStream` constructed with a byte[] parameter, write operations at the end of a `MemoryStream` expand the `MemoryStream`.