WIP: parameterise operators with boolean result by the result integer type

This PR parameterises Caesium's operators with a "boolean" result (i.e. the comparison operators as well as the derived && and || operators) by a result integer type (which was hard-coded before to i32) as a step to use Caesium for modelling other C-like languages with different modelling of boolean results (e.g. Rust, which uses single-byte booleans).

Concretely, the changes can be summarised as:

• add a parameter rit to the affected operators and use that for the operational semantics of these operators, replacing the i32 used before.
• adapt the existing notations for these operators to reflect this.
• add new derived notations in lang/c_notations.v that instantiate the operators with i32 so that the codegen for RefinedC does not need to be changed much, and change the Coq codegen to also import this new file.
• adapt the typing proofs to work for the changed operators instantiated to i32. Possibly, it might be desirable to support other result types even for C and to generalize the proofs accordingly, but I'm not sure.

The existing examples in the repo compile with these changes, but I haven't tested more exhaustively yet.

frontend/coq_pp.ml

@@ -300,7 +300,7 @@ let pp_code : string -> import list -> Coq_ast.t pp =
   let pp fmt = Format.fprintf ff fmt in
 
   (* Printing some header. *)
-  pp "@[<v 0>From refinedc.lang Require Export notation.@;";
+  pp "@[<v 0>From refinedc.lang Require Export notation c_notation.@;";
   pp "From refinedc.lang Require Import tactics.@;";
   pp "From refinedc.typing Require Import annotations.@;";
   List.iter (pp_import ff) imports;