Fix window frame keywords being parsed as implicit aliases

The PARTITION BY clause in window functions was incorrectly consuming
window frame keywords like ROWS, RANGE, GROUPS as implicit aliases.
This broke window function parsing for queries like:

  SELECT abs(number) over (partition by x rows unbounded preceding)

Added window frame keywords to the exclusion list in parseImplicitAlias:
- ROWS, RANGE, GROUPS (frame type)
- UNBOUNDED, PRECEDING, FOLLOWING, CURRENT (frame bounds)

Author: claude

parser/expression.go

@@ -180,6 +180,11 @@ func (p *Parser) parseImplicitAlias(expr ast.Expression) ast.Expression {
 		if upper == "INTERSECT" {
 			return expr
 		}
+		// Don't consume window frame keywords as implicit aliases
+		switch upper {
+		case "ROWS", "RANGE", "GROUPS", "UNBOUNDED", "PRECEDING", "FOLLOWING", "CURRENT":
+			return expr
+		}
 		alias := p.current.Value
 		p.nextToken()
 

parser/testdata/01571_window_functions/metadata.json

@@ -1,6 +1,5 @@
 {
   "explain_todo": {
-    "stmt12": true,
     "stmt3": true
   }
 }

parser/testdata/01591_window_functions/metadata.json

@@ -20,7 +20,6 @@
     "stmt38": true,
     "stmt39": true,
     "stmt41": true,
-    "stmt45": true,
     "stmt50": true,
     "stmt51": true,
     "stmt52": true,
@@ -39,7 +38,6 @@
     "stmt77": true,
     "stmt78": true,
     "stmt79": true,
-    "stmt8": true,
     "stmt80": true,
     "stmt81": true,
     "stmt82": true,