[#28] Make code conform to Serokell style policies

[dcastro]

Description

This PR refactors a few small things in the codebase and applies some of the guidelines outlined in code_style.

Since this PR touches many files, it's best to review it by reviewing one commit at a time (rather than everything at once).

Related issue(s)

Fixes #28

:white_check_mark: Checklist for your Pull Request

Related changes (conditional)

• Tests

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

• Documentation

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

• Public contracts

  • [ ] Any modifications of public contracts comply with the Evolution of Public Contracts policy.
  • [ ] I added an entry to the changelog if my changes are visible to the users and
  • [ ] provided a migration guide for breaking changes if possible

Stylistic guide (mandatory)

• [x] My commits comply with the policy used in Serokell.
• [x] My code complies with the style guide.