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/binder.rs

@@ -1,9 +1,9 @@
-use crate::ast::compiler::bound_nodes::{
+use crate::ast::nodes::{
     Address, AssignBinding, BoundPhase, DeclarationKind, DefBinding, GlobalIdx,
-    IdentifierBinding, LambdaBinding, Node, NodeKind, UpvalueIdx, VirtualId,
+    IdentifierBinding, LambdaBinding, Node, NodeKind, SyntaxKind, SyntaxNode, Symbol,
+    UpvalueIdx, VirtualId,
 };
 use crate::ast::diagnostics::Diagnostics;
-use crate::ast::nodes::{SyntaxKind, SyntaxNode, Symbol};
 use crate::ast::types::{Identity, Purity, StaticType};
 use std::collections::HashMap;
 use std::rc::Rc;