Add object hook method to JsonfileReader

[JSCU-CNI]

This PR adds the method obj_hook to the JsonfileReader adapter. This allows implementations of JsonfileReader to modify object output without redefining the entire __iter__ method.

[codecov]

Codecov Report

❌ Patch coverage is 73.07692% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.11%. Comparing base (ff6a1f1) to head (e12cd94).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
flow/record/adapter/jsonfile.py	73.07%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #226      +/-   ##
==========================================
- Coverage   84.24%   84.11%   -0.13%     
==========================================
  Files          35       35              
  Lines        3745     3759      +14     
==========================================
+ Hits         3155     3162       +7     
- Misses        590      597       +7     

Flag	Coverage Δ
unittests	84.11% <73.07%> (-0.13%)	⬇️

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[yunzheng]

I don't see a real problem with adding this, but was curious what the use-case was besides the one shown in the unit test.