Refactor optimizer utilities

Removes unused `flatten_tuple` function from optimizer utilities. The
functionality was moved to the `Folder` struct, making it more
contextually appropriate. This change streamlines the utility module and
improves code organization.

src/ast/compiler/optimizer/mod.rs

@@ -8,4 +8,4 @@ pub use engine::Optimizer;
 pub use folder::Folder;
 pub use inliner::Inliner;
 pub use substitution_map::SubstitutionMap;
-pub use utils::{PathTracker, UsageInfo, flatten_tuple};
+pub use utils::{PathTracker, UsageInfo};