Optimize hot paths: Replace SimpleDateFormat, LinkedList, and string concatenation

[Copilot]

Identified and fixed performance anti-patterns in frequently-executed code paths.

Changes

• Draft_6455.getServerTime(): Replaced per-call SimpleDateFormat instantiation with static DateTimeFormatter (thread-safe, no allocation overhead)
• Draft_6455.translateFrame(): Changed LinkedList to ArrayList for better cache locality
• Draft_6455.toString(): Replaced string concatenation (+=) with StringBuilder
• ByteBufferUtils.getEmptyByteBuffer(): Return duplicates of static empty buffer instead of allocating new instances
• ByteBufferUtils.transferByteBuffer(): Eliminated redundant Math.min() call in branch where comparison result is known

Before:

private String getServerTime() {
  Calendar calendar = Calendar.getInstance();
  SimpleDateFormat dateFormat = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z", Locale.US);
  dateFormat.setTimeZone(TimeZone.getTimeZone("GMT"));
  return dateFormat.format(calendar.getTime());
}

After:

private static final DateTimeFormatter HTTP_DATE_FORMAT = 
    DateTimeFormatter.ofPattern("EEE, dd MMM yyyy HH:mm:ss z", Locale.US)
        .withZone(ZoneId.of("GMT"));

private String getServerTime() {
  return HTTP_DATE_FORMAT.format(ZonedDateTime.now(ZoneId.of("GMT")));
}

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• checkstyle.org

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

Identify and suggest improvements to slow or inefficient code

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