Support value variables in log output

[dmitrii-ubskii]

What is the goal of this PR?

We now handle the possibility of Values being returned as part of a ConceptMap. Retrieved pure values are not displayed in the graph view, but printed out as expected in the log view.

What are the changes implemented in this PR?

Closes #791

[typedb-bot]

PR Review Checklist

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Trivial Change

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