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};

src/ast.nim

@@ -337,6 +337,7 @@ type
       declImplMethods*: seq[Decl]
     of dkModule:
       declModuleName*: string
+      declModulePath*: seq[string]
       declModuleItems*: seq[Decl]
     of dkUse:
       declUsePath*: seq[string]
@@ -370,11 +371,12 @@ type
   # ---------------------------------------------------------------------------
   Module* = ref object
     name*: string
+    path*: seq[string]
     items*: seq[Decl]
 
 # Convenience constructors
-proc newModule*(name: string): Module =
-  result = Module(name: name)
+proc newModule*(name: string, path: seq[string] = @[]): Module =
+  result = Module(name: name, path: path)
 
 proc newBlock*(loc: SourceLocation): Block =
   result = Block(loc: loc)