Adds nullability annotations among other things

Adds nullability annotations for all methods
Fixes some nullability problems and inconsistencies
Gets rid of RelativeBlockVector's inner class
Changes RelativeBlockVector to a record
Simplifies FromTheEndTeleportation's storage, and makes it into a minimal record
Removes the putStringInList method
Gets rid of some primitive list usage
Fixes some incorrect method accessibility
Removes some redundancy in PortalOption

src/main/java/net/knarcraft/stargate/event/StargateCloseEvent.java

@@ -22,7 +22,7 @@ public class StargateCloseEvent extends StargateEvent {
      * @param portal <p>The portal to close</p>
      * @param force  <p>Whether to force the gate to close, even if set as always-on</p>
      */
-    public StargateCloseEvent(Portal portal, boolean force) {
+    public StargateCloseEvent(@NotNull Portal portal, boolean force) {
         super(portal);
 
         this.force = force;
@@ -51,6 +51,7 @@ public class StargateCloseEvent extends StargateEvent {
      *
      * @return <p>A handler-list with all event handlers</p>
      */
+    @NotNull
     public static HandlerList getHandlerList() {
         return handlers;
     }