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/mod.rs

@@ -1,21 +1,20 @@
-pub mod analyzer;
-pub mod binder;
-pub mod bound_nodes;
-pub mod captures;
-pub mod dumper;
-pub mod lambda_collector;
-pub mod macros;
-pub mod optimizer;
-pub mod specializer;
-pub mod lowering;
-pub mod type_checker;
-
-pub use binder::*;
-pub use bound_nodes::*;
-pub use captures::*;
-pub use dumper::*;
-pub use macros::*;
-pub use optimizer::*;
-pub use specializer::*;
-pub use lowering::*;
-pub use type_checker::*;
+pub mod analyzer;
+pub mod binder;
+pub mod captures;
+pub mod dumper;
+pub mod lambda_collector;
+pub mod macros;
+pub mod optimizer;
+pub mod specializer;
+pub mod lowering;
+pub mod type_checker;
+
+pub use crate::ast::nodes::*;
+pub use binder::*;
+pub use captures::*;
+pub use dumper::*;
+pub use macros::*;
+pub use optimizer::*;
+pub use specializer::*;
+pub use lowering::*;
+pub use type_checker::*;