Register Watchpoints

[Sightem]

This PR implements register watchpoints.

[adriweb]

I guess we have to figure out how we can benchmark this properly, now 😅

[adriweb]

@calc84maniac suggested using https://github.com/TheScienceElf/TI-84-CE-Raytracing as a benchmark, and after a few opts with the likely/unlikely macros, emulation speed reported by @Sightem is at ≈660%, while master is at ≈670%, approximately 1.5% slower now.

On my side, it's at ≈980% during the first half of the drawing on master, and ≈965% on this branch. Also about 1.5% slower.

Looks like the impact is very small :)

Good job, merging 👍