Remove async trait

[ufoscout]

Issue ticket

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Checklist before requesting a review

Code conventions

• I have performed a self-review of my code
• Every new function is documented
• Object names are auto explicative

Security

• The PR does not break APIs backward compatibility
• The PR does not break the stable storage backward compatibility

Testing

• Every function is properly unit tested
• I have added integration tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• IC endpoints are always tested through the canister_call! macro