fix(radio-group): handle null values in compareOptions and use compareWith for deselection

[rudrakshagarwal4200-ai]

Fixes #30560.

Description of Change

1. Null-safe compareOptions: When compareWith is specified as a string property name, accessing properties on null or undefined values threw a TypeError: Cannot read properties of null (reading ...). This occurs in forms where the model value is initially null or reset to null. Added a null/undefined check so currentValue == null || compareValue == null safely returns currentValue === compareValue.
2. compareWith equality for deselection and tabindex in radio-group:
   • onClick: Previously checked newValue !== currentValue. When object values are used with compareWith, different object references were never seen as equal, causing allowEmptySelection deselection to fail and re-selecting instead. Now uses isOptionSelected(currentValue, newValue, this.compareWith).
   • onKeydown: Space key check for deselection now uses isOptionSelected(this.value, current.value, this.compareWith).
   • setRadioTabindex: Uses isOptionSelected(value, radio.value, this.compareWith) to correctly locate the active radio button for object values.
3. Added e2e tests covering allowEmptySelection with compareWith object values and verifying compareWith does not throw when value is null.

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