fix for multiframe KITTY_SELFREF made it slooooooooooooooow

[dankamongmen]

The fix for #2143 led to unacceptable slowdown in the yield demo. On "grimes", my T580 laptop, the 2.4.0 release runs in 53.33s. Current master runs in 117.74s, almost a 100% slowdown! erp!

[dankamongmen]

backing off to KITTY_ANIMATION from KITTY_SELFREF recovers almost all of the performance; I'm disabling KITTY_SELFREF until we've dealt with this. i think i've got some ideas over in the comments of #2143.

[dankamongmen]

though guess what...bitmapstates has some broken frames for KITTY_ANIMATED, lolololol. nothing's simple. (wipes look broken)

[dankamongmen]

so ideas include (these all need inspection of the protocol to see if they'd work):

• writing the new frame to somehow replace the original frame, maintaining wipes (v. good)
• writing the new frame and then reflecting the existing wipes rather than reblitting them (less good)

[dankamongmen]

though guess what...bitmapstates has some broken frames for KITTY_ANIMATED, lolololol. nothing's simple. (wipes look broken)

we've got these just about handled with my latest fix.

[dankamongmen]

ok, figured out the KITTY_ANIMATION deal with bitmapstates. right now, we break on the third-from-last frame, aka the first "full square on right". we nail the last frame, the second "full square on right". we're sending r=2,c=1 to get this result. if i change it to r=1,c=2, we invert, nailing the first one, and missing the second. so yeah, we're not copying a nulled-out version into our auxvecs -- we're doing that correclty. we are writing a first frame with nulled cells. r=2,c=2 misses on both. r=1,c=1 misses all manner of things. r=1,c=2 breaks intro when we get to the right.

so i think we need to recognize whether we blitted the original frame with nulls. if we did, use r=1,c=2. otherwise, use r=2,c=1. wipe ought work either way, since it's not sensitive in this way to the original blit. we need this information on a per-sprixcell basis. we could just store this as an extra byte in each auxvec. i think that would get it.

[dankamongmen]

yep, works perfectly, w00t!