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/utils.rs

@@ -0,0 +1,18 @@
+use crate::ast::compiler::bound_nodes::{AnalyzedNode, BoundKind};
+
+pub fn flatten_tuple(node: AnalyzedNode, into: &mut Vec<AnalyzedNode>) {
+    match node.kind {
+        BoundKind::Tuple { elements } => {
+            for el in elements {
+                flatten_tuple(el, into);
+            }
+        }
+        BoundKind::Record { fields } => {
+            for (_, v) in fields {
+                flatten_tuple(v, into);
+            }
+        }
+        BoundKind::Nop => {}
+        _ => into.push(node),
+    }
+}