Support for Java 17 in jpf-core

JPF currently cannot fully analyze Java 17 programs that use sealed classes and records — two features now standard in modern Java. This project completes Java 17 support in jpf-core by fixing sealed class enforcement, adding full record support (classfile parsing, metadata storage, and execution), and producing a Java 17 audit document that maps all remaining gaps for future contributors. The work targets the java-17 branch and builds on an existing contribution to the codebase.