Remove debounce on dimension mapping state to reduce lag

[axelboc]

Baby step to address #1578

1. We first added debouncing on the dimension mapping state in Debounce dim mapping state to reduce fetching rate when slicing #888 to address [DimensionMapper] Be less eager to fetch when slicing #879.
2. In [DimensionMapper] Review debouncing of dim mapping state #920, we then realised that this also debounced the axis mappers (the D0/D1/.../Dn button groups), so we opened Debounce slicing without affecting UI responsiveness #975 with the goal of moving the debounce to the sliders.
3. Turns out that in that PR, we added debouncing to the sliders without actually removing it on the dimension mapping state... So we ended up with two debounces, for a total of 350 ms.

In this PR, I therefore remove the debounce on the dimension mapping state, thus saving 100ms both when slicing and changing axis dimensions.

[loichuder]

Sorry for the delay. Well spotted 👍