[#426] Keep MorleyLogs in WriterT in interpreter

Description

Currently MorleyLogs are kept in StateT, and this design has some flaws.

This MR moves MorleyLogs to a dedicated WriterT layer.

Probably the same thing should be done for Integrational framework (and so for Cleveland), I'm leaving this for #461 (closed). If such change is not necessary for that issue, then we can live without it in our testing frameworks for now.

Related issue(s)

Resolves #426 (closed)

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