🐛 NumberBox initial value is not formatted

[bdlukaa]

Describe the bug
When the NumberBox.format function is provided, the initial box value is not formatted, only the values set after an interaction.

To Reproduce
Steps to reproduce the behavior:

1. Create a NumberBox and provide a format function
2. Set a value
3. See the error

Expected behavior
The initial value should be formatted.

Additional context
#1152 (comment)