refactoring!: make cargo clipper pass in pedantic mode

Our CI linter uses 'cargo clippy -- -Dclippy::all -Wclippy::pedantic'
command that previously failed due to multiple errors and warnings.
Current commit fixes all of them and make linter pass. The price
was high - some functions changed their API, some structures were
renamed. But all the warnings and errors seemed reasonable, so I
believe it is not a big deal now.