kryo5 upgrade

[Aklakan]

Work in progress.

GitHub issue resolved (no issue created yet).

Pull request Description: Upgrade to kryo5. Need yet to test whether spatial indexes created with kryo4 can be loaded with kryo5. Also, there was an inconsistent use of ConcurrentHashMap and LinkedHashMap that was revealed when a test case failed with kryo5.
In my first experiments I was not able to load a spatial index created with kryo4 using kryo5.

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See the Apache Jena "Contributing" guide.

[Aklakan]

I was not able to load a spatial-index created with kryo4 using kryo5 - it fails to deserialize the ConcurrentHashMap whose registration was missing. Kryo4 auto-registered classes in that case, whereas kryo5 by default requires registration. There is a flag kryo5.setRegistrationRequired(false); but this does not make loading work.

The question is whether to schedule a kryo5 upgrade for Jena6.

[afs]

The question is whether to schedule a kryo5 upgrade for Jena6.

Probably, yes. It is safer.

A major version change to Jena comes every 2 years when the supported java version changes so the opportunity is now.

Running both, while possible, is a maintenance cost.

Even if Kryo4 works now, bug fixes and security fixes will likely be to kryo5 first. I don't see much development around kryo4.

Choosing Kryo5 does not impact applications using Kryo4 elsewhere in their codebase.