[TM-9] Add macros unit tests

Description

Problem: Morley.Macro logic is untested.

Solution: write some unit tests for basic functions from Morley.Macro.

Tests for PAPAIR, UNPAPAIR, CADR, SET_CADR, MAP_CADR are based on language specification. Tests for mapLeaves cover some typical function behavior.

Related issue(s)

https://issues.serokell.io/issue/TM-9

✅ Checklist for your Merge Request

Related changes (conditional)

• Tests

  • If I added new functionality, I added tests covering it.
  • If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.

• Documentation

  • I checked whether I should update the docs and did so if necessary:
    • README
    • Haddock

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