fix(VNumberInput): keep all decimals when precision is null

Intl.NumberFormat defaults maximumFractionDigits to 3 (for plain numbers)

fixes #22990

Author: J-Sek

packages/vuetify/src/components/VNumberInput/__tests__/format.spec.ts

@@ -34,6 +34,11 @@ describe('format', () => {
       expect(formatNumber(1.23456, opts({ precision: 2 }))).toBe('1.23')
     })
 
+    it('keeps all decimals when precision is null', () => {
+      expect(formatNumber(0.1234, opts({ precision: null }))).toBe('0.1234')
+      expect(formatNumber(1234.12345678, opts({ useGrouping: 'auto', precision: null }))).toBe('1,234.12345678')
+    })
+
     it('respects minFractionDigits', () => {
       expect(formatNumber(1.2, opts({ minFractionDigits: 3 }))).toBe('1.200')
     })

packages/vuetify/src/components/VNumberInput/format.ts

@@ -47,7 +47,7 @@ export function formatNumber (val: number, options: FormatNumberOptions): string
       minimumFractionDigits: minFractionDigits && precision != null
         ? Math.min(minFractionDigits, precision)
         : (minFractionDigits ?? precision ?? undefined),
-      maximumFractionDigits: precision ?? undefined,
+      maximumFractionDigits: precision ?? 20, // Intl defaults are dynamic (0, 2, 3)
       useGrouping: options.useGrouping,
     })