Improvements to nitty-gritty details

Version 1.57.0 adds some new improvements and enhancements:

• Improvements to the way the difficulty is estimated for new puzzles generated by the puzzle generator.
• Improvements to the way the built-in help chooses the hint to show, so that easier steps are identified before more difficult steps.
• The built-in help now identifies a square with a pencilled block outline as being incorrect if the square will ultimately contain a number when the puzzle is completed.
• Added more auto-complete functionality for when a clue value is tapped and the associated row or column already has two blocks, or when the number of missing blocks exactly matches the number of empty squares. In particular, if a group of squares are selected by tapping the clue value and all squares have values except for one, the last square is promoted to a value if it only has one candidate value. The same also applies to the squares outside the blocks, when the selection is inverted.
• If a row or column with a hidden clue has two blocks, the squares between the blocks now get selected when the space is tapped where the clue would normally be shown. A second tap inverts the selection. If any number combinations were already showing, they remain showing and are no longer cleared.
• Enhancements to full dark appearance when dark mode is in operation. The panel showing the number combinations is less bright, the spotlight feature is shown with more contrast.
• Some cosmetic improvements to the number buttons (the round buttons for number values).
• Fix for an issue where number combinations were sometimes being filtered out incorrectly when the setting “only show combinations with the right numbers of values” is turned on.
• The level controls in the puzzle generator settings are less fiddly to adjust.