Bytes implementation

[virgil-serbanuta]

Bytes values should be held in a configuration cell, and we should provide hooks to access them. The Rust code should see only the IDs of these values. These hooks should be callable as normal Rust functions, but their implementation should work with the bytes cell.

We need hooks for:

• creating an empty bytes value
• bytes length
• concatenating bytes
• extracting substrings
• testing equality
• converting to/from Rust values (ints, Int256, Strings)

The Bytes struct will hold the bytes ID (u32).

We will add a Bytes trait that has: Empty(), FromId(u32), len(self), substr(self, start, end), appendTo(self, Bytes), equalTo(self, Bytes). Perhaps also toU8(self), toU16(self), ... and fromU8(u8), fromU16(u16), ...

We will also need the following:

syntax Expression ::= bytesStructFromKBytes(Expression)  [strict]
rule bytesStructFromKBytes(wrapped(B:Bytes)) => newStruct(bytesType, addBytesAndReturnId(B) , .CallParamsList)

syntax Expression ::= addBytesAndReturnId(Bytes)

rule <k> addBytesAndReturnId(B:Bytes) => ptrValue(null, u32(NextId)) ... <k>
     <buffers> Bs => Bs[NextId <- B] </buffers>
     <next-buffer-id> NextId => NextId +Int 1 </...>

and something similar for

syntax Expression ::= kBytesStructFromStructBytes(Expression)  [strict]