Optimize StringBuilder initialization in CorrelationIdFormatter

Initialize StringBuilder with the expected capacity (this.blank.length())
to avoid unnecessary resizing and array copying during string construction.

The blank field already contains the exact length needed for the formatted
output, making it an ideal initial capacity. This improves performance for
correlation ID formatting, which is frequently called during logging
operations.

See gh-48125

Signed-off-by: gobeomjun <alap_u@naver.com>

Author: K-jun98

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/CorrelationIdFormatter.java

@@ -85,7 +85,7 @@ private CorrelationIdFormatter(List<Part> parts) {
 	 * @return a formatted correlation id
 	 */
 	public String format(UnaryOperator<String> resolver) {
-		StringBuilder result = new StringBuilder();
+		StringBuilder result = new StringBuilder(this.blank.length());
 		formatTo(resolver, result);
 		return result.toString();
 	}