Fix lazy import of optional cbor2 package

[RalfG]

Fixed

• 🐛 io.cbor: Fixed lazy import of optional cbor2 package.

[codecov]

Codecov Report

❌ Patch coverage is 63.63636% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.23%. Comparing base (678dc3d) to head (af68ba7).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
psm_utils/io/cbor.py	60.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #136      +/-   ##
==========================================
- Coverage   72.25%   72.23%   -0.02%     
==========================================
  Files          32       32              
  Lines        3219     3224       +5     
==========================================
+ Hits         2326     2329       +3     
- Misses        893      895       +2     

Flag	Coverage Δ
unittests	72.23% <63.63%> (-0.02%)	⬇️

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