Added

Beta feature: 'Fast Finishing Mode' to rapidly fill cells at the end of the game. Fill squares with one pencil mark by short tap after three filled with long tap.
This is an opt-in beta feature, feel free to try out via preferences and report any feedback. The core feature (rapidly entering numbers) should already work, the mechanism to activate it is still in flow.
The ui elements blocking the keypad are far from finished, but functional and highly visible. (idea from mueller-ma and stella-sf)
The grid ui with yellow contrast color will likely not be changed.
Add a bunch of calculated difficulties to let the user choose which difficulty he/she wants to play. Calculated til now: All square game variants up to 9x9 with advanced settings untouched.

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