Fix panic when running on x86_64

The length of usize::to_be_bytes depends on the size of the pointer on the
targeted cpu architecture

src/types/packet.rs

@@ -1,4 +1,4 @@
-use core::convert::TryInto;
+use core::convert::{TryFrom, TryInto};
 
 use crate::constants::*;
 
@@ -119,7 +119,11 @@ impl From<DataBlock<'_>> for RawPacket {
         let len = block.data.len();
         packet.resize_default(10 + len).ok();
         packet[0] = 0x80;
-        packet[1..][..4].copy_from_slice(&len.to_le_bytes());
+        packet[1..][..4].copy_from_slice(
+            &u32::try_from(len)
+                .expect("Packets should not be more than 4GiB")
+                .to_le_bytes(),
+        );
         packet[5] = 0;
         packet[6] = block.seq;