Refactor: Move inlining logic to Inliner struct

Introduces the `Inliner` struct to encapsulate logic related to value
and function inlining. This improves code organization and readability
within the optimizer engine.

Key changes include:
- Moving `is_inlinable_value` to the `Inliner` struct.
- Extracting beta-reduction preparation logic into
  `Inliner::prepare_beta_reduction`.
- Moving parameter slot collection to
  `Inliner::collect_parameter_slots`.
- Introducing `flatten_tuple` to a new `utils` module, used by both
  `Folder` and `Inliner`.

src/ast/compiler/optimizer/folder.rs

@@ -4,6 +4,8 @@ use crate::ast::types::{Purity, StaticType, Value};
 use std::cell::RefCell;
 use std::rc::Rc;
 
+use super::utils::flatten_tuple;
+
 pub struct Folder<'a> {
     pub globals: &'a Option<Rc<RefCell<Vec<Value>>>>,
 }
@@ -54,7 +56,7 @@ impl<'a> Folder<'a> {
         }
 
         let mut arg_nodes = Vec::new();
-        self.flatten_tuple(args.clone(), &mut arg_nodes);
+        flatten_tuple(args.clone(), &mut arg_nodes);
         let mut arg_values = Vec::with_capacity(arg_nodes.len());
         for node in arg_nodes {
             if let BoundKind::Constant(val) = node.kind {
@@ -77,21 +79,5 @@ impl<'a> Folder<'a> {
         };
         Some(self.make_constant_node(result, callee))
     }
-
-    fn flatten_tuple(&self, node: AnalyzedNode, into: &mut Vec<AnalyzedNode>) {
-        match node.kind {
-            BoundKind::Tuple { elements } => {
-                for el in elements {
-                    self.flatten_tuple(el, into);
-                }
-            }
-            BoundKind::Record { fields } => {
-                for (_, v) in fields {
-                    self.flatten_tuple(v, into);
-                }
-            }
-            BoundKind::Nop => {}
-            _ => into.push(node),
-        }
-    }
 }
+