Add PARTITION and PART clause support for CHECK TABLE

The CHECK TABLE statement supports PARTITION and PART clauses to check
specific partitions or parts. Added these fields to the AST and parser.

Fixed test: 00961_check_table/stmt20

Author: claude

ast/ast.go

@@ -880,6 +880,8 @@ type CheckQuery struct {
 	Position  token.Position `json:"-"`
 	Database  string         `json:"database,omitempty"`
 	Table     string         `json:"table"`
+	Partition Expression     `json:"partition,omitempty"`
+	Part      Expression     `json:"part,omitempty"`
 	Format    string         `json:"format,omitempty"`
 	Settings  []*SettingExpr `json:"settings,omitempty"`
 }

parser/parser.go

@@ -7081,6 +7081,18 @@ func (p *Parser) parseCheck() *ast.CheckQuery {
 		check.Table = tableName
 	}
 
+	// Parse optional PARTITION clause
+	if p.currentIs(token.PARTITION) {
+		p.nextToken() // skip PARTITION
+		check.Partition = p.parseExpression(LOWEST)
+	}
+
+	// Parse optional PART clause
+	if p.currentIs(token.IDENT) && strings.ToUpper(p.current.Value) == "PART" {
+		p.nextToken() // skip PART
+		check.Part = p.parseExpression(LOWEST)
+	}
+
 	// Parse optional FORMAT
 	if p.currentIs(token.FORMAT) {
 		p.nextToken() // skip FORMAT

parser/testdata/00961_check_table/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt20": true
-  }
-}
+{}