video/epic12.cpp: Improved CV1000 blitter timings based on hardware t…

…esting, and removed unsafe mode. (#10849)

* Fixed an off-by-one bug when setting dst_x_end and dst_y_end which caused destination writes to be one pixel too big.
* Corrected calculations to utilize both source and destination VRAM row counts.
* Updated VRAM access overhead.
* Track of when blitter is idle, since long sequences of clipped draws can cause the blitter to not do any work while remaining busy.
* Removed the edge case for "pixel widths need to be evenly divisable by 8" until more examples can be studied.
* Pad draws to even 4-byte boundaries, since VRAM accesses are always 4 pixels at the time.
* Also added documentation for 6 unhandled Blitter command offsets (see blitter_w). Thanks rtw for looking at these.
* misc/cv1k.cpp: Updated some notes.