Improve testing and contributing

Usage related changes

Remove redundant artifact - replaced with utility function
Minimize a sierra artifact
Improve contribution guidelines (should have been done before OD Hack, but better late than never)
Improve Background{Devnet,Anvil}:
- Use shorter for loop instead of while
- Reuse client used for connection checking

[x] Checked the relevant parts of development docs
[x] Applied formatting - ./scripts/format.sh
[x] No linter errors - ./scripts/clippy_check.sh
[x] No unused dependencies - ./scripts/check_unused_deps.sh
[x] No spelling errors - ./scripts/check_spelling.sh
[x] Performed code self-review
[x] Rebased to the latest commit of the target branch (or merged it into my branch)
[x] Updated the docs if needed, including the TODO section
[x] Linked the issues which this PR resolves
[x] Updated the tests if needed; all passing (execution info)