fix hash issue with znjson serialization

[PythonFZ]

The zn.Hash did not use znjson.ZnEncoder which could lead to issues, e.g. if a parameter used a dataclass.

[codecov]

Codecov Report

Merging #305 (2ddfc91) into main (7ad2c49) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #305      +/-   ##
==========================================
+ Coverage   71.49%   71.51%   +0.02%     
==========================================
  Files          29       29              
  Lines        1319     1320       +1     
  Branches      262      262              
==========================================
+ Hits          943      944       +1     
  Misses        346      346              
  Partials       30       30              

Flag	Coverage Δ
unittests	71.51% <100.00%> (+0.02%)	⬆️

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Impacted Files	Coverage Δ
zntrack/core/dvcgraph.py	67.87% <100.00%> (+0.16%)	⬆️

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