Add frame parsing to WINDOW clause definitions

The WINDOW clause parser (parseWindowDefinitions) was missing
support for frame specifications (ROWS/RANGE/GROUPS). This meant
named window definitions like:

  WINDOW w1 AS (ROWS UNBOUNDED PRECEDING)

would fail to parse correctly.

Added frame parsing after ORDER BY in parseWindowDefinitions,
matching the logic in parseWindowSpec().

Author: claude

parser/parser.go

@@ -4551,6 +4551,14 @@ func (p *Parser) parseWindowDefinitions() []*ast.WindowDefinition {
 			}
 		}
 
+		// Parse frame specification (ROWS/RANGE/GROUPS)
+		if p.currentIs(token.IDENT) {
+			frameType := strings.ToUpper(p.current.Value)
+			if frameType == "ROWS" || frameType == "RANGE" || frameType == "GROUPS" {
+				spec.Frame = p.parseWindowFrame()
+			}
+		}
+
 		p.expect(token.RPAREN)
 		def.Spec = spec
 		defs = append(defs, def)

parser/testdata/01591_window_functions/metadata.json

@@ -11,23 +11,6 @@
     "stmt110": true,
     "stmt111": true,
     "stmt112": true,
-    "stmt31": true,
-    "stmt34": true,
-    "stmt35": true,
-    "stmt36": true,
-    "stmt37": true,
-    "stmt38": true,
-    "stmt39": true,
-    "stmt41": true,
-    "stmt50": true,
-    "stmt51": true,
-    "stmt52": true,
-    "stmt53": true,
-    "stmt54": true,
-    "stmt55": true,
-    "stmt56": true,
-    "stmt57": true,
-    "stmt69": true,
     "stmt70": true,
     "stmt71": true,
     "stmt72": true,

parser/testdata/02020_exponential_smoothing/metadata.json

@@ -1,7 +1 @@
-{
-  "explain_todo": {
-    "stmt32": true,
-    "stmt33": true,
-    "stmt35": true
-  }
-}
+{}

parser/testdata/03210_lag_lead_inframe_types/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt5": true
-  }
-}
+{}