Migrate nullability annotations to jSpecify

Mojang has done that, we don't need 3 different sets of annotations

src/main/java/carpet/script/exception/BreakStatement.java

@@ -2,7 +2,7 @@ package carpet.script.exception;
 
 import carpet.script.value.Value;
 
-import javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 
 public class BreakStatement extends ExitStatement
 {

src/main/java/carpet/script/exception/ContinueStatement.java

@@ -2,7 +2,7 @@ package carpet.script.exception;
 
 import carpet.script.value.Value;
 
-import javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 
 public class ContinueStatement extends ExitStatement
 {

src/main/java/carpet/script/exception/ExitStatement.java

@@ -2,7 +2,7 @@ package carpet.script.exception;
 
 import carpet.script.value.Value;
 
-import javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /* Exception thrown to terminate execution mid expression (aka return statement) */
 public class ExitStatement extends StacklessRuntimeException

src/main/java/carpet/script/exception/ExpressionException.java

@@ -6,7 +6,7 @@ import carpet.script.Token;
 import carpet.script.external.Carpet;
 import carpet.script.value.FunctionValue;
 
-import javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;

src/main/java/carpet/script/exception/Throwables.java

@@ -1,6 +1,6 @@
 package carpet.script.exception;
 
-import javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 import java.util.HashMap;
 import java.util.Map;