Add M5UnitUnified driver (UnitRTC as UnitPCF8563) and examples for UnitRTC

[GOB52]

Changes

New: M5UnitUnified Driver (UnitPCF8563)

• Full PCF8563/BM8563/HYM8563 driver built on M5UnitComponent
• Date/Time, Alarm, Countdown Timer, Clock Control, CLKOUT, and VoltLow APIs
• Alarm/Timer IRQ via polling (I2C) or hardware interrupt (GPIO)
• M5Unified M5.RTC compatible API (setDateTime, getDateTime, setAlarmIRQ, etc.)

New: Examples

• NTPSync — WiFi NTP sync → RTC, display local time
• AlarmNotify — Alarm callback with sprite-based display
• PeriodicTimer — Countdown timer with repeat/oneshot modes

I2C: 3-way Initialization

• NessoN1: SoftwareI2C via M5HAL
• NanoC6: M5.Ex_I2C
• Other boards: Standard Wire

Infrastructure

• CI workflows, board definitions, .clang-format, Doxyfile, ISSUE_TEMPLATE
• platformio.ini with 18+ board targets
• M5UnitUnified dependency >=0.4.1