chore: coding guidelines and apply to code.

[Daanvdplas]

• Change CI to cargo +nightly fmt. This brings advantages such as formatting comments and dependencies.
• Create coding guidelines in this repo.

EDIT:

• Replaced the todo's related to pop api to workspace dependencies to a separate issue refactor: pop api workspace dependencies #206 .
• Replaced the todo regarding scale inconsistency in refactor: scale inconsistency #209

If its already included in your work please continue and we can manage both issues in your PR.

[evilrobot-01]

* [ ]  pop-api and primitives to workspace dependencies

Need to consider the effects of this when publishing to crates.io

[Daanvdplas]

Need to consider the effects of this when publishing to crates.io

That shouldn't be a problem. Have been working with ink-sandbox (crate) and it uses workspace dependencies (ref)

[Daanvdplas]

Closed by #184