progress() is called in setPixelColor(), calculating the transition progress for each pixel. Replaced that call with an inline function to get the new segment variable.
The progress is updated in service() when handleTransition() is called.
The new variable is in a spot where padding is added, so this should not use more RAM.
Result: over 10% increase in FPS on 16x16 matrix
* removed IRAM_ATTR: `updateTransitionProgress()` is called only once per frame, no need to put it in RAM.
* changed transitionprogress to static, private variable, this is now more aligned with other variables using the same logic
* added inline: the function is only used in one place
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