fix: don't reserve space for trailing divider

[CatsDeservePets]

• Refs [Feature Request] Border Spacing option #2190

[CatsDeservePets]

This might not be the right way after all. Instead, the getWidths() function should be updated.

[joelim-work]

This might not be the right way after all. Instead, the getWidths() function should be updated.

I agree, the divider should not be part of the width of each window. So wtot should be reduced by the number of windows - 1 before calculating the ratios. If drawbox is enabled, then another two spaces should be taken out as they will be used for the left and right borders.

Also getWidths could be unit tested (maybe move to misc.go?), and the global options could be passed in as parameters.