fix: preserve OVER clause during window function rewriting

Two fixes for window function execution:

1. Parser fix: Fixed "order by order by" duplication in WindowSpec.Format()
   - The OrderBy.Format() method adds its own "order by" prefix
   - WindowSpec.Format() was also adding "order by" before calling OrderBy
   - Changed to iterate OrderBy items directly without the prefix

2. Execution layer fix: Preserve OVER clause during AST function rewriting
   - Added node.Over = newNode.Over in 5 astvisit files:
     - query_rewriting.go
     - from_rewrite.go
     - fragment_rewriting.go
     - internally_routable_typing.go
     - provider_string_extract.go
   - Without this, window functions lost their OVER clause during rewriting

Author: claude

internal/stackql-parser-fork/go/vt/sqlparser/ast.go

@@ -1987,7 +1987,13 @@ func (node *WindowSpec) Format(buf *TrackedBuffer) {
 		if needsSpace {
 			buf.WriteString(" ")
 		}
-		buf.astPrintf(node, "order by %v", node.OrderBy)
+		// Don't use %v for OrderBy as OrderBy.Format adds its own "order by" prefix
+		buf.WriteString("order by ")
+		prefix := ""
+		for _, n := range node.OrderBy {
+			buf.astPrintf(node, "%s%v", prefix, n)
+			prefix = ", "
+		}
 		needsSpace = true
 	}
 	if node.Frame != nil {