dev: group Kakarot entrypoints in dedicated files

[ClementWalter]

Why

Currently, the Kakarot contract is one single file with all the entry points.

As the contract gets bigger, it becomes difficult to read and understand what does what.

What

Create several sub contract with meaningful entrypoints

1. eth
2. config
3. messaging
4. admin

keep in the main kakarot.cairo only the constructor and imports all the functions defined in the other sub contracts (presets)

The simple getter and setter defined in the library.cairo should also be directly inlined in the corresponding entry points

(e.g.

@view
func get_native_token{syscall_ptr: felt*, pedersen_ptr: HashBuiltin*, range_check_ptr}() -> (
    native_token_address: felt
) {
    return Kakarot.get_native_token();
}

should be inlined in Kakarot.get_native_token)

[ClementWalter]

This is partially done (see #1352) we could do the others as well. tbd