fix(VDatePicker): fix crash when select date range with external adapter

[SonTT19]

Description

fixes #19330

Markup:

<template>
  <v-container>
    <v-row justify="space-around">
      <v-date-picker color="primary" multiple="range"></v-date-picker>
    </v-row>
  </v-container>
</template>

use date-io/dayjs adapter

import { createVuetify } from 'vuetify'
import DayJsAdapter from '@date-io/dayjs'

export const vuetify = createVuetify({
  date: { adapter: DayJsAdapter },
})

[johnleider]

Message me on Discord please, ty!

[KaelWD]

This should default to ms too

vuetify/packages/vuetify/src/composables/date/adapters/vuetify.ts

Lines 430 to 439 in d0136e0

	function getDiff (date: Date, comparing: Date | string, unit?: string) {
	const d = new Date(date)
	const c = new Date(comparing)
	if (unit === 'month') {
	return d.getMonth() - c.getMonth() + (d.getFullYear() - c.getFullYear()) * 12
	}
	return Math.floor((d.getTime() - c.getTime()) / (1000 * 60 * 60 * 24))
	}