gh-142349: Fix ast.unparse for lazy import statements (#144893)

The unparser was not handling the `is_lazy` attribute on Import and
ImportFrom AST nodes, causing lazy imports to be unparsed as regular
imports. This broke the round-trip (parse → unparse → reparse) for
any file containing `lazy import` statements.

Author: pablogsal

Lib/_ast_unparse.py

@@ -239,11 +239,11 @@ def visit_NamedExpr(self, node):
             self.traverse(node.value)
 
     def visit_Import(self, node):
-        self.fill("import ")
+        self.fill("lazy import " if node.is_lazy else "import ")
         self.interleave(lambda: self.write(", "), self.traverse, node.names)
 
     def visit_ImportFrom(self, node):
-        self.fill("from ")
+        self.fill("lazy from " if node.is_lazy else "from ")
         self.write("." * (node.level or 0))
         if node.module:
             self.write(node.module)