Refactor Solidity types in view call library to be defined in `.sol` files instead of using the `sol!` macro

[nategraf]

One rough edge in the view call library is that the BlockCommitment type is defined only in the Rust source code through a sol! macro. As a result, it is difficult to use in Solidity smart contracts to build upon it. Moving BlockCommitment and any other Solidity types into contracts that can be imported into smart contract projects would improve the developer experience.