Gets rid of `orig_palette`, we now always have only 2 palettes:
1. `logical_palette`
This palette has color cycling / swapping applied but no global
effects such as brightness / fade-in.
2. `system_palette`
This palette is the actual palette used for rendering.
It is usually `logical_palette` with the global brightness setting
and fade-in/out applied.
Additionally, we now keep the k-d tree around and use it to
update single colors.
The colors that are color-cycled / swapped are never included
in the k-d tree, so the tree does not need updating on color
cycles/swaps.
Uses a k-d tree to quickly find the best match
for a color when generating the palette blending
lookup table.
https://en.wikipedia.org/wiki/K-d_tree
This is 3x faster than the previous naive approach:
```
Benchmark Time CPU Time Old Time New CPU Old CPU New
-----------------------------------------------------------------------------------------------------------------------------------
BM_GenerateBlendedLookupTable_pvalue 0.0002 0.0002 U Test, Repetitions: 10 vs 10
BM_GenerateBlendedLookupTable_mean -0.7153 -0.7153 18402641 5239051 18399111 5238025
BM_GenerateBlendedLookupTable_median -0.7153 -0.7153 18403261 5239042 18398841 5237497
BM_GenerateBlendedLookupTable_stddev -0.2775 +0.3858 2257 1631 1347 1867
BM_GenerateBlendedLookupTable_cv +1.5379 +3.8677 0 0 0 0
OVERALL_GEOMEAN -0.7153 -0.7153 0 0 0 0
```
The distribution is somewhat poor with just 3 levels, so this can be improved further.
For example, here is the leaf size distribution in the cathedral:
```
r0.g0.b0: 88
r0.g0.b1: 10
r0.g1.b0: 2
r0.g1.b1: 32
r1.g0.b0: 27
r1.g0.b1: 4
r1.g1.b0: 12
r1.g1.b1: 81
```
Gleb Mazovetskiy