[#396] Resolve TODOs

Description

Problem: Over time, a certain amount of TODOs has accumulated in our repository. Some of them don't fit the format which we introduced in !981 (merged). We need to resolve/fix existing TODOs to avoid unnecessary warnings from danger bot, and then merge !981 (merged) to keep our TODOs in uniform and consistent format.

Solution:

• Existing TODOs are brought to a format that corresponds to our style guide.
• Created appropriate tickets for TODOs without issue ids.
• Removed TODOs which are already resolved.

Related issue(s)

Resolves #396 (closed)

✅ Checklist for your Merge Request

Related changes (conditional)

• Tests (see short guidelines)

  • 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:
    • Root README and other README.md files
    • Haddock
    • docs/
  • I updated changelog files of all affected packages released to Hackage if my changes are externally visible.

Stylistic guide (mandatory)

• My commits comply with the following policy.
• My code complies with the style guide.