fix: Number component incorrectly uses label as validator key

[77media-creations]

Problem

The Number component's processValidations method overwrites the $fieldKey
parameter with the component's label string:

$fieldKey = $this->label() ?? $this->key();

This means the validator's data array is keyed by the label (e.g. "Wash Temp")
instead of the actual FormIO field key (e.g. washTemp).

When a user submits an empty optional number field, submissionValue() returns
null. Laravel's Arr::has finds the label-key directly in the data (since it
contains no dots), so the numeric rule fires on null, producing a spurious
validation error: "The Wash Temp must be a number."

Odd side effect: Labels ending with a dot (e.g. "Rinse Temp.") happen to
avoid the error — Laravel's Arr::has treats dots as nested key separators, so it
looks for data["Rinse Temp"][""] which doesn't exist, and the numeric rule
never fires. This made the bug appear inconsistent and hard to trace.

Fix

Two changes, modelled after the existing Currency component which handles this
correctly:

1. Remove the $fieldKey override — use the parameter as passed in from
   BaseComponent::validate(), which is already $this->key().
2. Add nullable for non-required fields — so that a null submission value
   does not trigger the numeric rule (same pattern as Currency).

Tests

Added two cases to NumberTest::validationsProvider() covering empty optional
fields (both null and empty string).

[dxnter]

Thanks!

I think CI is misconfigured for forks, but I've verified that tests are passing

[nie7321]

Thank you!