PHP 8.1+ compatibility: Undefined array key "unsigned" and "type" in NumericTypeBase.php causing performance degradation

Problem/Motivation

In PHP 8.1 and higher, the custom_field module triggers multiple "Undefined array key" warnings within NumericTypeBase.php. These occur because the class attempts to access settings keys such as 'unsigned' and 'type' directly without verifying if they exist in the settings array.

While these are warnings, they can lead to extreme performance degradation (up to 60-second timeouts) in environments where error handlers (like Sentry or OpenSearch) are active. This is especially prevalent on forms with high-cardinality fields, as a single AJAX "Add more" action rebuilds all existing items, triggering hundreds of warnings and backtrace captures in a single request.

Steps to reproduce

1. Use an environment running PHP 8.1 or later.
2. Create or use an existing entity with a custom field type that includes at least one numeric subfield (e.g., Integer).
3. Add multiple items to this field (e.g., cardinality of 10+).
4. Perform an AJAX action on the form (like clicking "Add another item").
5. Check the Drupal watchdog logs for Warning: Undefined array key "unsigned" in Drupal\custom_field\Plugin\CustomField\FieldType\NumericTypeBase::getDefaultMinValue().

Proposed resolution

Update src/Plugin/CustomField/FieldType/NumericTypeBase.php to use null-coalescing operators or !empty() checks when accessing settings keys that may not be explicitly set in older configurations or migrated data.

Remaining tasks

• Review the attached patch.
• Verify that warnings are silenced on PHP 8.1+.
• Ensure no regression in logic for fields where 'unsigned' is explicitly set to TRUE.

User interface changes

None.

API changes

None.

Data model changes

None. The patch only adds safety checks for runtime array access.