Add virtual RTC persistence and emulator save states

[ATEMVEGETA]

This restores the original first-pass version from the previous PR after I accidentally deleted/reset the branch while cleaning up later experimental commits.

This PR branch contains only:
b3667e9 Add virtual RTC persistence and emulator save states

The later RTC/RAM-editing experiments were intentionally removed and are not included here.

Changes included:

• Persist RTC state in a .rtc sidecar and account for real elapsed host time while closed.
• Advance RTC from wall-clock time while running, so fast-forward does not speed up the clock.
• Add emulator state save/load support in a .state sidecar.
• Save/restore CPU, RAM, IO, timers, RTC registers, display controller state, EEPROM contents/state, accelerometer state, SSU, and SCI3 state.
• Add optional --no-menu launch flag for hiding the Qt menu bar.

Notes:

• This is a first pass intended for review and cleanup.
• The goal is to better match real Pokewalker behavior, where the device does not fully shut down between sessions.
• Save-state persistence also helps preserve state around day rollover behavior.