Correct Label Gun clear-action tooltip modifier and add regression coverage

[Copilot]

The Label Gun tooltip was expected to document modifier-click behavior (e.g., ctrl/alt combinations), but the clear-label hint showed the wrong modifier. This updates the tooltip wiring so on-hover guidance matches actual keybind behavior.

• Tooltip mapping fix

  • In LabelGunItem.appendHoverText, the clear reminder now references LABEL_GUN_CLEAR_MODIFIER_KEY instead of LABEL_GUN_PULL_MODIFIER_KEY.
  • This aligns the displayed combo with the clear action semantics.

• Regression guard

  • Added LabelGunTooltipTests to assert the clear tooltip reminder stays wired to the clear modifier key in source, preventing accidental key regression in future edits.

lines.add(
    LABEL_GUN_ITEM_TOOLTIP_CLEAR_REMINDER.getComponent(
        SFMKeyMappings.getKeyDisplay(SFMKeyMappings.LABEL_GUN_CLEAR_MODIFIER_KEY),
        SFMKeyMappings.getKeyDisplay(options.keyUse)
    ).withStyle(ChatFormatting.GRAY)
);