fix: move cipher to decryption function

[Ernst79]

HA was failing in the config flow tests with 2.13.0 on this part of the code when using encryption

assert self.cipher is not None  # nosec

I move the cipher part down to the decryption function. Not sure is this is the best way to solve it, but the HA tests do work with this change.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.10 ⚠️

Comparison is base (e6c192c) 77.66% compared to head (93c8baa) 77.56%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #82      +/-   ##
==========================================
- Coverage   77.66%   77.56%   -0.10%     
==========================================
  Files           6        6              
  Lines         479      477       -2     
  Branches       72       71       -1     
==========================================
- Hits          372      370       -2     
  Misses         83       83              
  Partials       24       24              

Impacted Files	Coverage Δ
src/bthome_ble/__init__.py	100.00% <100.00%> (ø)
src/bthome_ble/parser.py	83.49% <100.00%> (-0.11%)	⬇️

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[bdraco]

Is the bindkey getting set outside of init ?

[bdraco]

Ideally we don't want to recreate the object every time we decrypt a packet as it will likely be MUCH slower

[bdraco]

I fixed it in #83

[Ernst79]

Ideally we don't want to recreate the object every time we decrypt a packet as it will likely be MUCH slower

Yes, that what I also thought, but couldn't think of a better solution. Thanks!