feat: The Arity.of(int, int) return NAry when arguments are the same.

src/main/java/cz/jirutka/rsql/parser/ast/Arity.java

@@ -55,7 +55,7 @@ public interface Arity {
      * @return the created arity
      */
     static Arity of(int min, int max) {
-        return new DynamicArity(min, max);
+        return min == max ? nary(min) : new DynamicArity(min, max);
     }
 
     /**

src/test/groovy/cz/jirutka/rsql/parser/ast/AritySpec.groovy

@@ -0,0 +1,41 @@
+/*
+ * The MIT License
+ *
+ * Copyright 2026 Edgar Asatryan <nstdio@gmail.com>.
+ *
+ * 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 cz.jirutka.rsql.parser.ast
+
+import spock.lang.Specification
+
+class AritySpec extends Specification {
+    def 'should create N-ary object of arguments are equal'() {
+        given:
+        def n = 1
+
+        when:
+        def actual = Arity.of(n, n)
+
+        then:
+        actual instanceof NAry
+        actual.min() == n
+        actual.max() == n
+    }
+}