big sixel speedups incoming

[dankamongmen]

A lot of work has gone into #2573 recently, with big wins finally emerging.

3.0.5 allrgb: 13.045, 13.024, 13.141
master allrgb: 11.818, 11.827, 11.849
they-already-shrunk allrgb: 10.939, 10.957, 10.927

3.0.5 data: 18.047, 17.899, 17.921
master data: 16.445, 15.938, 16.030
they-already-shrunk data: 15.552, 16.170, 16.411

3.0.5 mkv: 2m48.019
master mkv: 1m37.331
they-already-shrunk mkv: 1m21.510(!)

for some of these (e.g. the allrgb images) you have libz/ffmpeg eating up ~50% of the original realtime, so there's not much i could do about that. trimmed a healthy amount of the remaining notcurses fat, though!

[dankamongmen]

these speedups hold over to real-life scenarios. here's notcurses-demo's [intro] and [xray]:

they-already-shrunk

             runtime│ frames│output(B)│    FPS│%r│%a│%w│TheoFPS║                
══╤════════╤════════╪═══════╪═════════╪═══════╪══╪══╪══╪═══════╣                
 1│   intro│   3.61s│    220│   3.75Mi│   61.0│ 0│ 0│43│ 136.63║                
 2│   intro│   3.63s│    220│   3.72Mi│   60.6│ 0│ 0│43│ 134.63║                
 3│   intro│   3.60s│    220│   3.72Mi│   61.1│ 0│ 0│43│ 136.88║                
 4│   intro│   3.60s│    219│   3.72Mi│   60.8│ 0│ 0│43│ 135.46║                
 5│    xray│  15.50s│    452│  42.40Mi│   29.2│ 0│ 0│41│  70.17║                
══╧════════╧════════╪═══════╪═════════╪═══════╧══╧══╧══╧═══════╝                
              29.94s│   1331│  57.32Mi│                                         

master

             runtime│ frames│output(B)│    FPS│%r│%a│%w│TheoFPS║                
══╤════════╤════════╪═══════╪═════════╪═══════╪══╪══╪══╪═══════╣                
 1│   intro│   3.84s│    220│   3.62Mi│   57.4│ 0│ 0│46│ 119.68║                
 2│   intro│   3.82s│    220│   3.59Mi│   57.6│ 0│ 0│46│ 120.80║                
 3│   intro│   3.80s│    219│   3.59Mi│   57.7│ 0│ 0│46│ 120.96║                
 4│   intro│   3.83s│    219│   3.58Mi│   57.3│ 0│ 0│46│ 119.73║                
 5│    xray│  15.51s│    430│  34.30Mi│   27.7│ 0│ 0│40│  67.04║                
══╧════════╧════════╪═══════╪═════════╪═══════╧══╧══╧══╧═══════╝                
              30.78s│   1308│  48.68Mi│                                         

3.0.5

             runtime│ frames│output(B)│    FPS│%r│%a│%w│TheoFPS║                
══╤════════╤════════╪═══════╪═════════╪═══════╪══╪══╪══╪═══════╣                
 1│   intro│   3.90s│    220│   3.63Mi│   56.4│ 0│ 0│47│ 115.88║                
 2│   intro│   3.84s│    220│   3.60Mi│   57.3│ 0│ 0│46│ 119.69║                
 3│   intro│   3.85s│    221│   3.59Mi│   57.4│ 0│ 0│46│ 119.69║                
 4│   intro│   3.89s│    220│   3.59Mi│   56.6│ 0│ 0│47│ 115.94║                
 5│    xray│  15.52s│    366│  26.84Mi│   23.6│ 0│ 0│27│  85.97║                
══╧════════╧════════╪═══════╪═════════╪═══════╧══╧══╧══╧═══════╝                
              30.99s│   1247│  41.24Mi│                                         

[dankamongmen]

that 85.97 for [xray] on 3.0.5 is just a weirdness of TheoFPS. look at the true FPS numbers:

• 3.0.5: 23.6
• master: 27.7
• they-already-shrunk: 29.2