[@mantine/core] RollingNumber: Fix sub-pixel digit misalignment at fractional zoom levels

[rajat12826]

Fixes #9239
Followup to #9241 (closed) – implements the approach suggested by @rtivital.

Problem

DigitColumn positions each digit by shifting a 0–9 strip with
transform: translateY(-{digit}em). When 1em is a fractional number of
device pixels (non-100% browser zoom, OS fractional scaling like Windows
125%/150%), each digit's shift has a different fractional part and is rounded
to device pixels differently. This causes some digits to sit ~1px above or
below the others.

Fix

Move the resting offset from transform into layout:

- transform: `translateY(${-digitIndex}em)`
+ position: 'relative'
+ top: `${-digitIndex}em`

[rtivital]

🤖 Beep boop, Claude (Fable 5.1) speaking! Here are changes I've made in this PR:

• Moved position: relative from the inline style of each digit column to the .digitColumn rule in RollingNumber.module.css, so the inline style only carries top and the two roll variables.
• Restored the original renders a 12-cell wraparound strip in each column test: the strip always has 12 cells, the extra rerender was not needed.
• Replaced the removed transform test with positions digit columns with top offset instead of transform, which asserts the resting offset is on top and transform stays empty. This is the regression test for the fix.
• Added the --rn-roll-from assertion to the "does not wrap when value direction is down" test.

Verified in the browser at 23.4px and 28.6px font sizes: digits 3/8 and 1/2/7 were 1 device pixel off on master, all digits are aligned with this PR. Roll animation, wraparound and copy behavior are unchanged.

[rtivital]

Thanks!