In Java bindings, delete more local references

[jtraglia]

Teku shared with me that their memory usage with ckzg is higher than expected (~10gb). I believe the issue is that we were not properly deleting local references.

[asn-d6]

Changes look sensible, but a bit hard to review due to the error cases that need to be handled.

What do you think about trying out a goto-based free strategy, like we do in the core library code?
The calls to DeleteLocalRef in the functions that can throw errors get quite complicated.
IIUC we could implement goto-based freeing since the docs say that localRef: a local reference. The function does nothing in the case of a NULL value passed here..

Also, have we tested that these changes fix the memleaks? Should we get a Teku devs to do some testing?

[tbenr]

I spent some time on this and I don't think those changes matter than much. We are not facing a memory leak issue here.

the relevant reading is this: https://docs.oracle.com/javase/7/docs/technotes/guides/jni/spec/design.html#wp1242

I don't think we fall into the situation in which is better to manually call DeleteLocalRef.

As per doc:
Local references are valid for the duration of a native method call, and are automatically freed after the native method returns.
This should be good enough for us.