Fix ByteBuf memory leak in MinecraftVarintFrameDecoder (#1715)

- Reset buffer reader index on exception to prevent memory leaks when packet decoding fails.

proxy/src/main/java/com/velocitypowered/proxy/protocol/netty/MinecraftVarintFrameDecoder.java

@@ -91,6 +91,7 @@ public class MinecraftVarintFrameDecoder extends ByteToMessageDecoder {
 
     // try to read the length of the packet
     in.markReaderIndex();
+    try {
       int length = readRawVarInt21(in);
       if (packetStart == in.readerIndex()) {
         return;
@@ -115,6 +116,11 @@ public class MinecraftVarintFrameDecoder extends ByteToMessageDecoder {
           out.add(in.readRetainedSlice(length));
         }
       }
+    } catch (Exception e) {
+      // Reset buffer to consistent state before propagating exception to prevent memory leaks
+      in.resetReaderIndex();
+      throw e;
+    }
   }
 
   private boolean validateServerboundHandshakePacket(ByteBuf in, int length) throws Exception {
@@ -122,6 +128,7 @@ public class MinecraftVarintFrameDecoder extends ByteToMessageDecoder {
         state.getProtocolRegistry(direction, ProtocolVersion.MINIMUM_VERSION);
 
     final int index = in.readerIndex();
+    try {
       final int packetId = readRawVarInt21(in);
       // Index hasn't changed, we've read nothing
       if (index == in.readerIndex()) {
@@ -150,6 +157,11 @@ public class MinecraftVarintFrameDecoder extends ByteToMessageDecoder {
 
       in.readerIndex(index);
       return false;
+    } catch (Exception e) {
+      // Reset buffer to consistent state before propagating exception to prevent memory leaks
+      in.readerIndex(index);
+      throw e;
+    }
   }
 
   @Override