private static LoadingCache<AsciiString, String> buildCache(String spec) {
        return Caffeine.from(spec).build(AsciiString::toString);
    }
Validator for the scheme part of the URI, as defined in
<a href="https://datatracker.ietf.org/doc/html/rfc3986#section-3.1">the section 3.1 of RFC3986</a>.
core/src/main/java/com/linecorp/armeria/internal/common/ArmeriaHttpUtil.java