v1.2.3

This release introduces the changes that were originally intended for version 1.2.2, which was mistakenly created from a branch other than main, so this version corrects that.

https://central.sonatype.com/artifact/io.github.malczuuu.problem4j/problem4j-core/1.2.3

1. Maven:

   <dependencies>
       <dependency>
           <groupId>io.github.malczuuu.problem4j</groupId>
           <artifactId>problem4j-core</artifactId>
           <version>1.2.3</version>
       </dependency>
   </dependencies>

2. Gradle (Kotlin DSL):

   dependencies {
       implementation("io.github.malczuuu.problem4j:problem4j-core:1.2.3")
   }

Fixed

• Fix missing Serializable iface and serialVersionUID to Problem.Extension and ProblemImpl.ExtensionImpl.
• Allow reducing boilerplate while checking for type being assigned by providing an isTypeNonBlank convenience method.

Changes: v1.2.1...v1.2.3