Update code styling rules

[ignas-k]

Is your feature request related to a problem? Please describe.

Currently the code styling rules are loose and subjective. It would be better to clearly define them all and enforce them properly. With strictly defined styling rules it would be easier for developers to write code correctly and the code would become more consistent across the whole repository. Additionally, it would be beneficial to review our current ESLint and Prettier rules e.g. import order, line gaps etc.

Describe the Solution you'd like

A few major tasks:

• Update STYLEGUIDE.md (and CONTRIBUTING.md if needed).
• Review ESLint and Prettier rules.
• Refactor existing code with the new rules.

TBA: smaller tasks for each category about specific styling rules

Describe alternatives you've considered

No response

Additional context

No response

[GerardasB]

Please update package.json fields and README.md as well.