Simplify Expressions

[rcosta358]

Overview

This PR aims to solve issue #58, by applying constant propagation and folding to the AST after a refinement error is found, to simplify the error message shown to the user.

This simplification is done in a way that allows simplification steps to be expanded or collapsed by keeping track of their origin nodes, which can later be used in the VS Code extension, by serializing the derivation tree to JSON.

Additions

• VariableResolver - extracts variables with constant values from the AST and stores them in a HashMap
• ConstantPropagation - substitutes variables with their constant values from that HashMap
• ConstantFolding - simplifies expressions by evaluating nodes with constant values
• ExpressionSimplifier - combines propagation and folding and simplifies the derivation tree by removing redundant conjuncts (e.g., x && true, x == x)
• DerivationNode, ValDerivationNode, BinaryDerivationNode, UnaryDerivationNode, VarDerivationNode - nodes that form the derivation tree
• ExpressionSimplifierTest - tests generated by Claude Sonnet 4.5

Example

public class Example {
    
    public static void requiresNegative(@Refinement("x < 0") int x) {}
    
    public static void example(int x) {
        int a = 6;
        int b = 2;
        requiresNegative((a / b + (-5)) + x);
    }
}

[alcides]

Looks good to me in general. There are a few minor points that you can take a look at, that might improve the code quality.

[rcosta358]

Thanks for the review!