Refactor: Replace optimization level with boolean flag

The optimizer now uses a simple boolean flag (`optimization`) instead of
an `optimization_level` (u32). This simplifies the optimizer's logic and
makes it easier to enable or disable optimizations.

The command-line interface and internal testing have been updated to
reflect this change.

src/bin/ast.rs

@@ -31,15 +31,15 @@ struct Cli {
     #[arg(short, long)]
     trace: bool,
 
-    /// Optimization level (0: None, 1: Cracking, 2: Aggressive)
-    #[arg(short, long, default_value_t = 0)]
-    opt: u32,
+    /// Disable optimization
+    #[arg(long)]
+    no_opt: bool,
 }
 
 fn main() {
     let cli = Cli::parse();
     let mut env = Environment::new();
-    env.optimization_level = cli.opt;
+    env.optimization = !cli.no_opt;
 
     if cli.bench || cli.update_bench {
         if cfg!(debug_assertions) {