Add cartridge banking, DMA, joypad, and ROM tests

[DanielCuevas1208]

Summary

• Add cartridge bank switching.
• Add DMA timing.
• Add joypad input.
• Add save data support.
• Add automated test ROM runs.

Review status

Do not merge yet.

The JOYP select bits use active-low logic. The current code uses active-high logic and does not return the stored select bits. Correct the register behavior and update its tests.

Validation

Run the unit tests, test ROMs, build, and headless checks after the correction.

[DanielCuevas1208]

Do not merge this revision yet. The Game Boy JOYP selection logic is reversed. Bits 4 and 5 are active-low, but Joypad.read() selects a column when the stored bit is nonzero. The returned register value also drops the stored select bits. Correct the register behavior and update the tests before merge. Keep the joypad interrupt test separate from the selection test.