Runtime functionality in MLIR

[gabrielbosio]

Migrating Runtime logic to MLIR may be useful to know how much reducing function call overhead may affect on contract execution performance.

One starting point is the Syscall Handler glue code, by making some arguments to be passed as reference form MLIR without converting them to Rust. This would imply:

• Exposing some structs #[repr(C)] for the MLIR -> Rust data
• Custom container that uses malloc for all the Rust -> MLIR logic