Add \a and \v escape sequence support and fix raw byte handling

- Add support for \a (bell, 0x07) and \v (vertical tab, 0x0B) escape
  sequences in the lexer's string parsing
- Fix escapeStringLiteral to iterate over bytes instead of runes to
  preserve raw bytes like \xAA that are not valid UTF-8

Enables test 00342_escape_sequences.

Author: claude

internal/explain/format.go

@@ -27,10 +27,12 @@ func FormatFloat(val float64) string {
 
 // escapeStringLiteral escapes special characters in a string for EXPLAIN AST output
 // Uses double-escaping as ClickHouse EXPLAIN AST displays strings
+// Iterates over bytes to preserve raw bytes (including invalid UTF-8)
 func escapeStringLiteral(s string) string {
 	var sb strings.Builder
-	for _, r := range s {
-		switch r {
+	for i := 0; i < len(s); i++ {
+		b := s[i]
+		switch b {
 		case '\\':
 			sb.WriteString("\\\\\\\\") // backslash becomes four backslashes (\\\\)
 		case '\'':
@@ -48,7 +50,7 @@ func escapeStringLiteral(s string) string {
 		case '\f':
 			sb.WriteString("\\\\f") // form feed becomes \\f
 		default:
-			sb.WriteRune(r)
+			sb.WriteByte(b)
 		}
 	}
 	return sb.String()

lexer/lexer.go

@@ -376,10 +376,14 @@ func (l *Lexer) readString(quote rune) Item {
 				sb.WriteRune('\r')
 			case '0':
 				sb.WriteRune('\x00')
+			case 'a':
+				sb.WriteRune('\a')
 			case 'b':
 				sb.WriteRune('\b')
 			case 'f':
 				sb.WriteRune('\f')
+			case 'v':
+				sb.WriteRune('\v')
 			case 'x':
 				// Hex escape: \xNN
 				l.readChar()

parser/testdata/00342_escape_sequences/metadata.json

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