Allow setting minimum scrollbar thumb height in vertical n-scrollbar

[lanyeeee]

Clear and concise description of the problem

I want set the minimum height for the scrollbar thumb in n-scrollbar, so that the scrollbar remains usable when working with n-virtual-list containing large datasets.

Currently, when using n-virtual-list with a large amount of data, the scrollbar thumb becomes extremely small due to the automatic height calculation based on content proportion, which affects user interaction and experience.

While issue #6456 allows customizing the width of vertical scrollbar and height of horizontal scrollbar through theming, it doesn't address the need to set the minimum height for the vertical scrollbar thumb itself.

Suggested solution

Add a new property y-bar-min-size to n-scrollbar to set the minimum height of the scrollbar thumb:

Usage example:

<n-virtual-list
style="max-height: 240px"
:item-size="42"
:items="items"
:scrollbar-props="{ yBarMinSize: 20 }"
>
<template #default="{ item }">
  <div :key="item.key" class="item" style="height: 42px">
    <img class="avatar" :src="item.avatar" alt="" />
    <span> {{ item.value }}</span>
  </div>
</template>
</n-virtual-list>

Alternative

No response

Additional context

No response

Validations

• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.