[TEST] Adding multiboxPrior test based on equivalent in deepjavalibrary/dlj

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Description

This PR adds a test for MultiboxPrior. This code is based on the deepjavalibrary.djl class:
https://github.com/deepjavalibrary/djl/blob/master/integration/src/main/java/ai/djl/integration/tests/modality/cv/MultiBoxPriorTest.java

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