improve BLData type hints

[tobiaslatour]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 96.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.54%. Comparing base (b5614ef) to head (02cf9f0).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
bletl/types.py	96.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #79      +/-   ##
==========================================
+ Coverage   93.30%   93.54%   +0.24%     
==========================================
  Files          11       11              
  Lines        1239     1239              
==========================================
+ Hits         1156     1159       +3     
+ Misses         83       80       -3     

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