misc: code optimisations and warnings fixes

[wthrajat]

Fixes various clippy code warnings by removing unnecessary stuff to optimize the codebase.

These includes warnings about operator precedence, redundant field names in struct initialization, single-character string constant used as pattern, unnecessary casting integer literal to u8, reference immediately dereferenced by the compiler, useless conversions, unnecessary let, return statements, closures etc.

Detailed clippy logs can be found here