refactor(parser): Step 4 - Extract items module

- Create items module with global_vars, functions, static_items
- Move parse_global_var from mod.rs to items/global_vars.rs
- Move parse_function_declaration to items/functions.rs
- Move parse_static_declaration and parse_static_function to items/static_items.rs
- Clean up mod.rs by removing 197 lines of code
- Build passes successfully

Next: Step 5 - Final cleanup and documentation

src/parser/items/mod.rs

@@ -0,0 +1,17 @@
+/*!
+ * Parser Items Module
+ * 
+ * Top-level item declarations:
+ * - Global variables
+ * - Function declarations
+ * - Static declarations (functions and boxes)
+ */
+
+pub mod global_vars;
+pub mod functions;
+pub mod static_items;
+
+// Re-export for convenience
+pub use global_vars::*;
+pub use functions::*;
+pub use static_items::*;