Fix save-state serialization of CPU dataBus and controller state

[SergioChan]

Summary

• add dataBus to CPU JSON serialization properties so open-bus state survives save/load
• add JSON serialization methods for Controller and include both controllers in NES save state payload
• restore controller state in NES.fromJSON() when present
• add a regression test ensuring cpu.dataBus and controller turbo/button state round-trip through save/load

Testing

• node --test test/nes.spec.js
• full npm test was not runnable in this environment because prettier is not executable (sh: 1: prettier: Permission denied)

Related

Fixes #614