Following discussion in #2847 this issue is the MVP of zero copy buffers, with foreign owned byte arrays over synchronous calls.

The frontends already detect:

• [ByRef] bytes in UDL
• &[u8] in proc-macros.

The foreign language bindings represent this as:

• Data for Swift
• ByteBuffer for Kotlin — this is a change in behaviour.
• bytes for Python

For arguments in async calls, this would revert to copying semantics.

For &mut [u8], this is slightly more involved:

• Introduce a [ByMutRef] bytes annotation in UDL
• Detect mutability in the proc macro, and error if async.
• Introduce a LiftMutRef trait to correspond to the LiftRef trait.
• alter the foreign language bindings:
  • inout Data for Swift
  • bytearray for Python

Without mutability, this would be more minimal, but non-viable.