feat(api): add PotentSulfur block entity representation

Additions:
- New BlockEntity interface for the potent sulfur geyser exposing
  the dormant/erupting countdown
- Keys.ERUPTION_COUNTDOWN (sponge-namespaced, Ticks-valued) backs
  the countdown value; pairs with BlockStateKeys.POTENT_SULFUR_STATE
  for the visible state flip.

See: https://minecraft.wiki/w/Potent_Sulfur

Author: gabizou

src/main/java/org/spongepowered/api/block/entity/PotentSulfur.java

@@ -0,0 +1,66 @@
+/*
+ * This file is part of SpongeAPI, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) SpongePowered <https://www.spongepowered.org>
+ * Copyright (c) contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package org.spongepowered.api.block.entity;
+
+import org.spongepowered.api.data.BlockStateKeys;
+import org.spongepowered.api.data.Keys;
+import org.spongepowered.api.data.value.Value;
+import org.spongepowered.api.util.Ticks;
+
+/**
+ * Represents a geyser-like, periodically erupting block that applies a
+ * nausea effect to nearby living entities while a suitable noxious source
+ * exists above it, and may launch entities upward during an eruption.
+ *
+ * <p>The countdown exposed by {@link #eruptionCountdown()} advances each
+ * server tick the block entity finds a valid source; when it elapses the
+ * block toggles between its dormant and erupting block-state forms (see
+ * {@link BlockStateKeys#POTENT_SULFUR_STATE}).</p>
+ *
+ * @see <a href="https://minecraft.wiki/w/Potent_Sulfur">Potent Sulfur</a>
+ */
+public interface PotentSulfur extends BlockEntity {
+
+    /**
+     * {@link Keys#ERUPTION_COUNTDOWN}
+     *
+     * <p>The remaining ticks until the next state flip. When the block
+     * entity has not yet evaluated its surroundings (or no suitable
+     * noxious source is present), this value is absent.</p>
+     *
+     * @return The mutable eruption countdown.
+     */
+    default Value.Mutable<Ticks> eruptionCountdown() {
+        return this.requireValue(Keys.ERUPTION_COUNTDOWN).asMutable();
+    }
+
+    /**
+     * Clears the eruption countdown, forcing the block entity to
+     * re-evaluate its surroundings on the next server tick.
+     */
+    default void resetCountdown() {
+        this.remove(Keys.ERUPTION_COUNTDOWN);
+    }
+}

src/main/java/org/spongepowered/api/data/Keys.java

@@ -1101,6 +1101,15 @@ public final class Keys {
      */
     public static final Key<Value<Ticks>> END_GATEWAY_AGE = Keys.key(ResourceKey.sponge("end_gateway_age"), Ticks.class);
 
+    /**
+     * The remaining ticks until a {@link org.spongepowered.api.block.entity.PotentSulfur}
+     * block entity toggles between its dormant and erupting states.
+     *
+     * <p>The value is absent when the block entity has not yet evaluated
+     * its surroundings or when no suitable noxious source is present.</p>
+     */
+    public static final Key<Value<Ticks>> ERUPTION_COUNTDOWN = Keys.key(ResourceKey.sponge("eruption_countdown"), Ticks.class);
+
     /**
      * The {@link EntityType entity type} of a spawn egg, which may be one of
      * several based on {@link ItemTypes#ZOMBIE_SPAWN_EGG}, etc. It is not