Allow host to pass reference types (&[u8] and &str) to guest funcs #1987

Sandbox::call only accepts owned string and byte arguments: String, Vec<u8> and Vec<Bytes>. Guest call_host has the same limit. Hyperlight never needs ownership, because arguments are only borrowed and copied once into the virtqueue. A user holding a &[u8] or &str must clone it first, for example sandbox.call("f", bytes.to_vec()), which costs an extra allocation and copy.

For bytes, users must also pick the type that matches the guest function's parameter:

• Vec<u8> (VecBytes): the guest copies the bytes into a Vec<u8>.
• Vec<Bytes> (ByteChunks): the guest keeps Bytes handles to the transport buffers without copying.

Fix:

• Accept &str and &[u8] arguments, and keep accepting owned ones.
• Send all byte arguments in one format, and let the guest function's parameter type decide how to read them. A Vec<Bytes> parameter keeps the transport buffers without copying, and a Vec<u8> parameter copies once.

Copies per byte argument: