Add price tooltips

src/main/kotlin/moe/nea/firmament/events/ItemTooltipEvent.kt

@@ -0,0 +1,17 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Linnea Gräf <nea@nea.moe>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+package moe.nea.firmament.events
+
+import net.minecraft.client.item.TooltipContext
+import net.minecraft.item.ItemStack
+import net.minecraft.text.Text
+
+data class ItemTooltipEvent(
+    val stack: ItemStack, val context: TooltipContext, val lines: MutableList<Text>
+) : FirmamentEvent() {
+    companion object : FirmamentEventBus<ItemTooltipEvent>()
+}