2.2.3 - auto zone processor cache invalidation; add SAMD21, SAMD51 back into Tier 1 suport

• 2.2.3 (2023-05-31, TZDB version 2023c)
  • Update ace_time/testing/* classes to support splitting the test data
    into 2 separate lists: transitions and samples.
    • Required to support new validation_data.json from AceTimeValidation.
  • Update AceTimeValidation test names to tests/Xxx{Basic,Extended}Test.
  • Add ZonedExtra::kAbbrevSize to define the char buffer size needed to
    hold an abbreviation.
  • Change ZonedExtra::kInvalidMinutes from public to private.
    • This is an implementation detail.
    • Use ZonedExtra::isError() instead.
  • Rename AceTimePython to acetimepy.
  • ZoneProcessor transition cache
    • Save the epoch year, and automatically invalidate and regenerate the
      cache when the Epoch::currentEpochYear() is modified.
    • Remove cache invalidation methods which are no longer needed:
      • ZoneProcessor::resetTransitionCache()
      • ZoneProcessorCache::resetZoneProcessors()
      • ZoneManager::resetZoneProcessors()
  • Rename "Converter Epoch" to "Internal Epoch".
    • Change daysToCurrentEpochFromConverterEpoch() to
      daysToCurrentEpochFromInternalEpoch().
    • This is an internal implementation detail, exposed only for testing
      purposes.
  • Update supported boards and tiers
    • Add SAMD21 and SAMD51 boards to Tier 1
      • Add Adafruit ItsyBitsy M4 (SAMD51 120MHz ARM Cortex-M4)
      • SAMD21 and SAMD51 boards are back in Tier 1, as long as they use
        the traditional Arduino API instead of the new
        Arduino-Core.
      • Fortunately most third party SAMD21 and SAMD51 boards continue to
        use the traditional Arduino API.
    • Move Teensy 3.2 to Tier 2
      • This board is entering end-of-life.
      • As well, the Teensyduino environment integrates with the Arduino
        IDE and CLI in a way that's different than all other third-party
        Arduino boards. Some of my automation scripts do not work with
        Teensyduino, so it becomes very time consuming to test the Teensy
        boards.
      • All Teensy boards are now in Tier 2 ("Should work but not tested
        often").