State serialization gaps: CPU dataBus, controller state not saved

[bfirsh]

Summary

CPU dataBus not serialized

cpu.js JSON_PROPERTIES does not include dataBus. The open bus value resets to 0 on save state restore. Games reading open bus immediately after a load could behave differently.

Controller state not serialized in NES.toJSON()

nes.js:177-185 serializes CPU, PPU, PAPU, and mapper state but not controller state. Button states, turbo state, and strobe protocol state are lost on save/restore. While usually minor (buttons are transient), the strobe state matters for correct controller reads immediately after restoring.

Fix

Add dataBus to CPU.JSON_PROPERTIES and serialize controller state in NES.toJSON()/NES.fromJSON().