2.4.0 - support %z; upgrade to TZDB 2024b

• 2.4.0 (2024-12-13, TZDB version 2024b)
  • Support new %z value in FORMAT column.
  • Upgrade TZDB to 2024b
    • https://lists.iana.org/hyperkitty/list/[email protected]/thread/IZ7AO6WRE3W3TWBL5IR6PMQUL433BQIE/
    • "Improve historical data for Mexico, Mongolia, and Portugal. System V
      names are now obsolescent. The main data form now uses %z. The code
      now conforms to RFC 8536 for early timestamps. Support POSIX.1-2024,
      which removes asctime_r and ctime_r. Assume POSIX.2-1992 or later for
      shell scripts. SUPPORT_C89 now defaults to 1."
• 2.3.2 (2024-07-25, TZDB version 2024a)