Fix best sales slider column sizing

[CySSoO]

Motivation

• The last slide in the Prettyblock Best Sales slider could wrap into two rows instead of staying on a single carousel slide.
• The column width calculation used ceil(12 / x), which could produce column classes that make the total width exceed 12 and cause wrapping.
• A minimum column width is required to avoid generating col-0 classes when items_per_slide is greater than 12.

Description

• Replace {math equation="ceil(12 / x)" ...} with {math equation="floor(12 / x)" ...} for mobile, tablet and desktop column width calculations in views/templates/hook/prettyblocks/prettyblock_best_sales.tpl.
• Add guards that set each computed column width to 1 when the result is less than 1 to prevent zero-width columns.
• The change updates how productColumnClasses are built so slides no longer overflow their row width.

Testing

• No automated tests were run for this change.

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Codex Task