MudComboBoxItem: Disabled items can still be selected by clicking #659

Bug description

MudComboBoxItem does not prevent selection when Disabled is set to true.

Although disabled items are visually marked and excluded from eligible item lists, clicking a disabled item can still change the selected value.

Root cause

MudComboBoxItem.HandleOnClick() does not check the Disabled state before calling MudComboBox.ToggleOption().

Additionally, ToggleOption() does not independently reject disabled items.

Expected behavior

• Disabled items must not be selectable through mouse interaction.
• Clicking a disabled item must not change the ComboBox selection.
• Disabled items must not trigger selection-related callbacks.

Suggested fix

Ensure disabled items cannot initiate selection through HandleOnClick(), and consider enforcing the same restriction in ToggleOption() to protect the selection logic consistently.

Regression test

A regression test has already been introduced in PR #656:

ComboBox_DisabledItemShouldNotBeSelectable

The test is currently marked with [Ignore] to document the known issue without breaking CI.

Once fixed, the test should be enabled and verified.

Credits

This issue was discovered during the expanded ComboBox and ComboBoxItem test coverage contributed in #656.

Thanks to @Yomodo for the valuable contribution and for identifying an existing behavioral bug while improving our test coverage!