refactor: move low level layer into BTHomeData

[IvoGruber]

Moved more low level functions into BTHomeData and marked those as "private" using "_".

Also moved to get_encrypted_payload and get_nounce to BTHomeData.

Note: Also fixed undocumented mac feature. Guess I broke it with previous pull request.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.21%. Comparing base (f5341c8) to head (99a1177).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #332      +/-   ##
==========================================
+ Coverage   81.89%   83.21%   +1.31%     
==========================================
  Files           6        6              
  Lines         685      685              
  Branches      101      101              
==========================================
+ Hits          561      570       +9     
+ Misses         98       88      -10     
- Partials       26       27       +1     

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[Ernst79]

Thanks again. Looks good.