Add Nano Every ATmega4809 register compatibility

[ChristRm]

Summary

This adds explicit support for Arduino Nano Every / ATmega4809 builds that use Arduino's 328 register emulation compatibility layer.

The existing ATmega4809 implementation uses native PORTx.DIRSET, PORTx.OUTCLR, and PORTx.IN register access. That works when compiling with Registers emulation = None (ATMEGA4809), but fails when Arduino's compatibility mode exposes PORTB as PORTBClass, where members like .IN, .DIRSET, and .OUTCLR are not available.

This change keeps the existing native ATmega4809 path untouched and adds a compatibility path using VPORTx when AVR_NANO_4809_328MODE or UNO_WIFI_REV2_328MODE is defined.

Why

This preserves support for current ATmega4809 raw-register builds while allowing Nano Every compatibility-mode builds to compile without PORTBClass errors.

Verified

• Arduino Nano Every
• ATmega4809
• Registers emulation = None (ATMEGA4809)
• Sketch compiles and uploads successfully

[kalymos]

It's good that it's a version 9 release, but the BIOS patch timers still need to be addressed. Hopefully, they'll be identical to the 328.
Otherwise we'll have to start all over again with the logic analyzer.
I hope you're not in too much of a hurry; I won't be home until the end of the month, and I wanted to have a little more fun with the port on the RP2040s.

[ChristRm]

It's good that it's a version 9 release, but the BIOS patch timers still need to be addressed. Hopefully, they'll be identical to the 328.

Otherwise we'll have to start all over again with the logic analyzer.

I hope you're not in too much of a hurry; I won't be home until the end of the month, and I wanted to have a little more fun with the port on the RP2040s.

I am not in hurry because after soldering the wires to my PS-18 motherboard my Playstation does not run any disks even if I don't plug those wires to the Arduino controller. Once I fix the problem I will be able to test the code from the current PR, but it will not be earlier than in 2 weeks

[kalymos]

The RP version only has the LED, the serial port, and the card generation detection that are currently functional. There's no point in rushing things, and it could lead to significant changes.