Replace Vec<u8> with slices &[u8] as function parameters

[matjazv]

Description

• if a function has slice as parameter, it could accept both slices or Vectors as its argument
• Check if any function could accept a fixed size array as a parameter instead of a slice (eg. &[u8; 32] instead of &[u8]). In this case a compiler could verify if a function call has a valid value as argument.

Acceptance Criteria

• functions have slices &[u8] as parameters instead of vectors Vec<u8>

Additional Information

• only perform this two actions on a places in the code where and if it makes sense