fix(VSlider): correct roundValue when min is not a multiple of step

[hellozzm]

Summary

When min is not a multiple of step (e.g., min=0.1, step=1), the roundValue function in useSteps incorrectly computes min % step as an offset, causing floating point rounding errors. For example, a thumb at value 25 would display as 25.1 instead of 25.

The fix computes the number of steps from min and builds the rounded value from there, avoiding the offset-based approach entirely.

Playground Markup

<template>
  <v-app>
    <v-container style="max-width: 400px">
      <p>With bug: thumb should show 25, not 25.1</p>
      <v-slider
        :min="0.1"
        :max="100"
        :step="1"
        thumb-label
        model-value="25"
      ></v-slider>
      
      <p class="mt-4">Another example: min=0.3, step=1, value=10</p>
      <v-slider
        :min="0.3"
        :max="50"
        :step="1"
        thumb-label
        model-value="10"
      ></v-slider>
    </v-container>
  </v-app>
</template>

<script setup>
</script>

Testing

1. Open the playground above
2. Check the first slider thumb label - it should show 25 (not 25.1)
3. Click on the slider and drag - values should snap to integers (0.1, 1.1, 2.1, ... no, to 0, 1, 2...)
4. Check the second slider - thumb should show 10 (not 10.3)
5. Before fix: first slider showed 25.1, second showed 10.3

Fixes #22348

[J-Sek]

Just stop posting PRs. We don't need this slop.