Assemble constModel in UtArrayModel if required

[EgorkaKulikov]

Description

The logic of AssembleModelGenerator is designed to traverse all models recursively and try to assemble them.

UtArrayModel has constModel field, but it is not involved in instance creation if all elements are set with stores. We should not assemble constModel in such case.

How to test

Automated tests

• The set of AssembleModelGeneratorTests
• Tests in arrays package of utbot-samples

Self-check list

• I've set the proper labels for my PR (at least, for category and component).
• PR title and description are clear and intelligible.
• I've added enough comments to my code, particularly in hard-to-understand areas.
• The functionality I've repaired, changed or added is covered with automated tests.
• Manual tests have been provided optionally.
• The documentation for the functionality I've been working on is up-to-date.