feat: optimize receiving messages

[unsafePtr]

Background

• Eliminated allocations: No more GetBuffer() calls that create new arrays for text messages
• Improved performance: Single reusable buffer instead of constantly requesting new streams
• Appropriate tool usage: RecyclableMemoryStream is designed for large streams, which is uncommon in WebSocket
  scenarios. ArrayBufferWriter is more suitable for typical WebSocket message sizes. RecyclableMemoryStream is still used when the user explicitly requests to receive messages as streams (IsStreamDisposedAutomatically = false), maintaining backward compatibility.