[WIP] Fix BinaryExporter deserialization for multiple UserData lists

[Copilot]

• Enable testLists=true in JmeExporterTest to reproduce the issue
• Investigate the BinaryInputCapsule index issue
• Identify root cause: Multiple UserData objects share BinaryClassObject and reuse field names/aliases
• Implement fix: Use serialized unique ID field to generate unique prefixes
• Address code review feedback: Use AtomicLong counter for guaranteed uniqueness
• Run tests to verify the fix works
• Request final code review

Original prompt

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This section details on the original issue you should resolve

<issue_title>BinaryExporter fails when serializing multiple UserData objects containing lists</issue_title>
<issue_description>I was playing around with @copilot and it says it found this issue: #2607 (comment)

Reporting here for tracking, but i haven't validated it yet.

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When a Spatial has multiple UserData entries containing lists (e.g., "int-list", "string-list", "float-list"), the BinaryExporter/BinaryImporter fails to deserialize correctly. The first list in the userData HashMap deserializes successfully, but subsequent lists return null and cause an ArrayIndexOutOfBoundsException during deserialization.

Steps to reproduce:

1. Set testLists=true in jme3-plugins/src/test/java/com/jme3/export/JmeExporterTest.java (line 142)
2. Run ./gradlew :jme3-plugins:test --tests "com.jme3.export.JmeExporterTest"
3. Observe that BinaryImporter (Node 1) returns null for int-list and string-list, while float-list works (being first in iteration order)

Error:

java.lang.ArrayIndexOutOfBoundsException: Index -3 out of bounds for length 4
    at com.jme3.export.binary.ByteUtils.rightAlignBytes(ByteUtils.java:554)
    at com.jme3.export.binary.BinaryInputCapsule.readInt(BinaryInputCapsule.java:834)
    at com.jme3.export.binary.BinaryInputCapsule.setContent(BinaryInputCapsule.java:154)

Notes:

• XMLExporter/XMLImporter works correctly with all lists
• Only affects BinaryExporter when multiple UserData objects with lists exist
• Appears to be a byte stream alignment issue in the binary format

</issue_description>

<agent_instructions>Validate the issue and if needed, propose a solution</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes BinaryExporter fails when serializing multiple UserData objects containing lists #2609

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