Add $ROWGUID pseudo-column support and enable MiscTests100 tests

- Extend lexer to recognize $ as identifier start when followed by a
  letter (for pseudo-columns like $ROWGUID)
- Add PseudoColumnRowGuid handling in parseAssignmentSetClause for
  UPDATE SET $ROWGUID = ... syntax
- Enable Baselines100_MiscTests100 and MiscTests100 tests

Author: claude

parser/lexer.go

@@ -466,7 +466,10 @@ func (l *Lexer) NextToken() Token {
 	case '\'':
 		tok = l.readString()
 	default:
-		if isLetter(l.ch) || l.ch == '_' || l.ch == '@' || l.ch == '#' {
+		// Handle $ only if followed by a letter (for pseudo-columns like $ROWGUID)
+		if l.ch == '$' && isLetter(l.peekChar()) {
+			tok = l.readIdentifier()
+		} else if isLetter(l.ch) || l.ch == '_' || l.ch == '@' || l.ch == '#' {
 			tok = l.readIdentifier()
 		} else if isDigit(l.ch) {
 			tok = l.readNumber()
@@ -516,7 +519,7 @@ func (l *Lexer) skipWhitespaceAndComments() {
 
 func (l *Lexer) readIdentifier() Token {
 	startPos := l.pos
-	for isLetter(l.ch) || isDigit(l.ch) || l.ch == '_' || l.ch == '@' || l.ch == '#' {
+	for isLetter(l.ch) || isDigit(l.ch) || l.ch == '_' || l.ch == '@' || l.ch == '#' || l.ch == '$' {
 		l.readChar()
 	}
 	literal := l.input[startPos:l.pos]

parser/parse_dml.go

@@ -832,12 +832,20 @@ func (p *Parser) parseAssignmentSetClause() (*ast.AssignmentSetClause, error) {
 		}
 	}
 
-	// col = value or col ||= value
-	col, err := p.parseMultiPartIdentifierAsColumn()
-	if err != nil {
-		return nil, err
+	// Check for $ROWGUID pseudo-column
+	if p.curTok.Type == TokenIdent && strings.EqualFold(p.curTok.Literal, "$ROWGUID") {
+		clause.Column = &ast.ColumnReferenceExpression{
+			ColumnType: "PseudoColumnRowGuid",
+		}
+		p.nextToken()
+	} else {
+		// col = value or col ||= value
+		col, err := p.parseMultiPartIdentifierAsColumn()
+		if err != nil {
+			return nil, err
+		}
+		clause.Column = col
 	}
-	clause.Column = col
 
 	if p.isCompoundAssignment() {
 		clause.AssignmentKind = p.getAssignmentKind()

parser/testdata/Baselines100_MiscTests100/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/MiscTests100/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}