Implement `cargo clippy`

[wkargul]

Why:

• get rid off common known mistakes and improve Rust code,
• implement clippy
• many lints appear when running clippy on current yagna (i.e. https://github.com/golemfactory/yagna/pull/2136) what helps catching bugs

What:

• run cargo clippy and solve issues in accordance with clippy hints (be carefull if fixing by cargo clippy --fix)
• adjust CI ???
• research on possible issues sfter implementing clippy

Notice:

• this should released no sooner than before yagna-v0.11 release as this must be tested profoundly