jextract: support returning JavaKit wrapped Java objects (Resolves #841)

[amanmaurya92]

Description

Resolves #841. This PR adds support for returning JavaKit-wrapped Java objects (like JavaLong or JavaString) from Swift functions back to Java.

Approach

• Type Detection: Updated translateResult, translateOptionalResult, and translateArrayResult in both NativeTranslation and JavaTranslation to recognize types passing the isSwiftJavaWrapper predicate.
• Java Shim: Maps the return type to the corresponding underlying Java class (e.g., java.lang.Long) rather than throwing an unsupported type error.
• Native Translation (C bindings): Returns the Swift value wrapped in an Optional, and calls .getJNIValue(in: environment) to safely extract and return the underlying JNI object reference (or NULL if missing).
• Tests: Added tests to JNIJavaKitTests for functions returning standard wrappers, optional wrappers, and arrays of wrappers.

[madsodgaard]

I haven't read the code, but please also add some runtime tests to the JNI sample app