gb: perform halt optimisations

[deltabeard]

This change is expected to make a minor improvement to performance.

On halt:

• Check if interrupts are enabled. If not, throw "Game halted forever" error.
• Calculate the number of cycles until the next interrupt is expected to occur.
• Apply the number of cycles to all of the peripherals (LCD, Timer, Serial, etc.).
• Handle interrupt.

This requires extensive testing to ensure game compatibility isn't reduced.

[deltabeard]

Work so far can be found in https://github.com/deltabeard/Peanut-GB/tree/halt_optimisations Frame rate increases when playing Pokemon Red on an RP2040 (with no display) was from 130 to 500 fps.

[deltabeard]

Merged. 8e0a61fcfd89259d179a28a48b9043ed324cbf6e