float32 hit pos, faster simd unpackAlphaValues

[guzba]

does not result in leaks per leak fuzzing tests

before: newImage(mask) ..................... 1.216 ms 1.246 ms ±0.040 x1000 svg decode ........................ 14.268 ms 14.358 ms ±0.108 x348 fill text .......................... 2.959 ms 3.004 ms ±0.037 x1000

after: newImage(mask) ..................... 0.828 ms 0.845 ms ±0.023 x1000 svg decode ........................ 13.982 ms 14.053 ms ±0.076 x356 fill text .......................... 2.955 ms 2.986 ms ±0.027 x1000