Preserve buffer positions during binary export

[ittaigolde]

Summary

• Preserve original NIO buffer positions when BinaryOutputCapsule writes FloatBuffer, IntBuffer, ByteBuffer, and ShortBuffer values
• Add a binary exporter regression test that verifies positions are unchanged and serialized contents still round-trip

Fixes #2312.

Testing

• ./gradlew.bat :jme3-core:test --tests com.jme3.export.binary.BinaryOutputCapsuleBufferPositionTest --no-daemon
• ./gradlew.bat :jme3-core:test --no-daemon

[gemini-code-assist]

Code Review

This pull request updates BinaryOutputCapsule to preserve the positions of NIO buffers (FloatBuffer, IntBuffer, ByteBuffer, and ShortBuffer) during serialization by wrapping the write operations in a try-finally block that restores the original position. It also adds a comprehensive unit test suite to verify this behavior. The reviewer suggests a cleaner approach: using absolute get(int index) instead of relative get(), which avoids mutating the buffer's position entirely and eliminates the need for the try-finally blocks.

[ittaigolde]

Could a maintainer please approve/run the gated GitHub Actions workflow for this fork PR? If the screenshot comment workflow fails, it appears to be the same infrastructure issue: Build jMonkeyEngine is gated for the fork PR, so the Run Screenshot Tests check is not created for the monitor workflow to wait on.

[Copilot]

Pull request overview

This PR fixes BinaryExporter buffer serialization so writing NIO buffers no longer mutates their current positions, aligning binary export behavior with the stated regression case for issue #2312.

Changes:

• Replaces relative buffer reads after rewind() with absolute indexed reads in BinaryOutputCapsule.
• Adds a regression test covering ByteBuffer, FloatBuffer, IntBuffer, and ShortBuffer position preservation and round-trip contents.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
jme3-core/src/plugins/java/com/jme3/export/binary/BinaryOutputCapsule.java	Preserves caller buffer positions while serializing buffer contents.
jme3-core/src/test/java/com/jme3/export/binary/BinaryOutputCapsuleBufferPositionTest.java	Adds regression coverage for buffer position preservation during binary export.

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[riccardobl]

Thank you! Nice find and patch 💯