feat: add stdlib module support with auto-import resolution

- Parse module paths in stdlib (module Std::Array { ... })
- Collect stdlib declarations and inject into user modules before sema
- Add dkExternFunc support throughout pipeline (parser, sema, hir, c backend)
- Auto-dereference pointer types for field access (arr->field)
- Add hArrowField HIR node for cleaner C emission
- Fix resolveTypeExpr for pointer and cast types
- Fix struct field lowering to use resolveTypeExpr
- Allow int <-> uint implicit conversion for bootstrap convenience
- Add stdlib/Std/Array.bux with dynamic array primitives
- Add stdlib_test demonstrating Array usage via import Std::Array::{Array};

stdlib_test/bux.toml

@@ -0,0 +1,7 @@
+[Package]
+Name    = "stdlib_test"
+Version = "0.1.0"
+Type    = "bin"
+
+[Build]
+Output = "Bin"

stdlib_test/src/Main.bux

@@ -0,0 +1,21 @@
+import Std::Array::{Array, Array_New, Array_Push, Array_Get, Array_Len, Array_Free};
+import Std::Io::{PrintLine, PrintInt};
+
+func Main() -> int {
+    var arr: Array = Array_New(4);
+    
+    Array_Push(&arr, 10);
+    Array_Push(&arr, 20);
+    Array_Push(&arr, 30);
+    
+    PrintLine("Array contents:");
+    var i: uint = 0;
+    while i < Array_Len(&arr) {
+        PrintInt(Array_Get(&arr, i));
+        PrintLine("");
+        i = i + 1;
+    }
+    
+    Array_Free(&arr);
+    return 0;
+}