DH-22326: Un-hide group-by columns, keep other hidden columns hidden when applying rollup

[vbabich]

Fix DH-22326: when applying a rollup, group-by columns now become visible while previously-hidden non-grouped columns stay hidden across the model swap. Replaces the previous showAllColumns() reset in handleRollupChange with a targeted metricCalculator.resetColumnWidth call for each group-by column, so the metric calculator's existing by-name width tracking handles preservation automatically. Also eliminates the brief flicker that the previous reset caused.

[github-actions]

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