Increase max regex length in SpEL expressions

This commit increases the max regex length in SpEL expressions from 256
to 1024 in order to support use cases where a regex may be rather long
without necessarily increasing the complexity of the regex.

Closes gh-30265

spring-expression/src/main/java/org/springframework/expression/spel/ast/OperatorMatches.java

@@ -47,7 +47,7 @@ public class OperatorMatches extends Operator {
 	 * Maximum number of characters permitted in a regular expression.
 	 * @since 5.2.23
 	 */
-	private static final int MAX_REGEX_LENGTH = 256;
+	private static final int MAX_REGEX_LENGTH = 1024;
 
 	private final ConcurrentMap<String, Pattern> patternCache;
 

spring-expression/src/test/java/org/springframework/expression/spel/EvaluationTests.java

@@ -484,15 +484,13 @@ void matchesWithPatternAccessThreshold() {
 
 		@Test
 		void matchesWithPatternLengthThreshold() {
-			String pattern = "(0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789" +
-					"0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789" +
-					"01234567890123456789012345678901234567890123456789|abc)";
-			assertThat(pattern).hasSize(256);
-			Expression expr = parser.parseExpression("'abc' matches '" + pattern + "'");
+			String pattern = "(%s|X)".formatted("1234".repeat(255));
+			assertThat(pattern).hasSize(1024);
+			Expression expr = parser.parseExpression("'X' matches '" + pattern + "'");
 			assertThat(expr.getValue(context, Boolean.class)).isTrue();
 
 			pattern += "?";
-			assertThat(pattern).hasSize(257);
+			assertThat(pattern).hasSize(1025);
 			evaluateAndCheckError("'abc' matches '" + pattern + "'", Boolean.class, SpelMessage.MAX_REGEX_LENGTH_EXCEEDED);
 		}