private static boolean isContinuation(int b) {
        return (b & 0xc0) == 0x80;
    }
Decodes the specified string from the index of {@code from} to the index of {@code toExcluded} if it's
<a href="https://datatracker.ietf.org/doc/html/rfc3986#section-2.1">Percent-Encoded</a>.
core/src/main/java/com/linecorp/armeria/internal/common/PercentDecoder.java