refactor: CodeClimate Improvements

[sleepdefic1t]

Summary

This PR resolves several code issues flagged in CodeClimate and Codacy.

Specifically, this PR does the following:

• hash.cpp
  • use memmove vs raw loop.
• crypto_helpers.h
  • add offset to join method.
  • add join w/offset test.
  • improve join test.
• serializer.cpp
  • use join w/offset vs raw loop.
  • use std::accumulate vs raw loops.
• transaction.cpp
  • initialize local vars in toArray() call.
  • use memmove vs strncpy & strncat.
  • use "%" PRIu32 vs "%d" in sprintf call.
  • use object.length() vs strlen.

Checklist

• Tests (if necessary)
• Ready to be merged

[sleepdefic1t]

@faustbrian good to go 👍