AVRSimulator never instantiated avr8js's AVREEPROM peripheral, so any
EEPROM.read/write/update hung the sketch: the Arduino EEPROM library spins
on `while (EECR & (1<<EEPE))` waiting for the write-complete bit to clear,
and with no peripheral driving EECR that bit never cleared (issue #203 —
EEPROM.update(0,123) + EEPROM.read(0) hangs instead of printing 123).
Wire AVREEPROM to the CPU in both loadHex() and reset() via a new
attachEeprom() helper. The EEPROMMemoryBackend is created once per
simulator instance and reused across firmware reloads and resets, so a
value written in one run is still readable on the next boot — matching
real hardware, where re-flashing leaves EEPROM intact. Sizes per variant
(Uno 1024 B, Mega2560 4096 B, ATtiny85 512 B); ATtiny85 gets its own
register map (EECR 0x3C / EEDR 0x3D / EEARL 0x3E / EEARH 0x3F) since
avr8js's default eepromConfig targets the ATmega328P.
Adds eeprom.test.ts: drives the EEPROM register protocol against the
production AVRSimulator (loadHex + step), asserting a byte round-trips,
the EEPE poll terminates (no hang), and contents survive a reset.
3f23a7950c