Refactor: Move compiler node definitions to src/ast/nodes

The `bound_nodes.rs` file has been removed and its contents have been
moved to `src/ast/nodes.rs`. This consolidates all AST node definitions
into a single module, improving organization and maintainability.

The `compiler` modules now import these definitions from
`crate::ast::nodes` instead of `crate::ast::compiler::bound_nodes`.

src/ast/compiler/optimizer/engine.rs

@@ -1,4 +1,4 @@
-use crate::ast::compiler::bound_nodes::{
+use crate::ast::nodes::{
     Address, AnalyzedNode, AssignBinding, GlobalAnalyzedRegistry,
     IdentifierBinding, LambdaBinding, Node, NodeKind, UpvalueIdx,
 };
@@ -756,7 +756,7 @@ impl Optimizer {
     }
 
     /// Extracts the address from a Def pattern node (when it's a simple Identifier with Declaration binding).
-    fn extract_def_addr(pattern: &AnalyzedNode) -> Option<Address<crate::ast::compiler::bound_nodes::VirtualId>> {
+    fn extract_def_addr(pattern: &AnalyzedNode) -> Option<Address<crate::ast::nodes::VirtualId>> {
         if let NodeKind::Identifier {
             binding: IdentifierBinding::Declaration { addr, .. },
             ..