jsonblob: Support individual record iteration

[jvdm]

Add a per-record iterator interface using rangefunc-style to jsonblob. This conveniently aligns jsonblob to be used with the Vulnerability and Enrichment datastore iterator interfaces.

[codecov]

Codecov Report

❌ Patch coverage is 78.57143% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.82%. Comparing base (0831b93) to head (ef03423).
⚠️ Report is 687 commits behind head on main.

Files with missing lines	Patch %	Lines
libvuln/jsonblob/jsonblob.go	78.57%	5 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1334      +/-   ##
==========================================
+ Coverage   55.76%   55.82%   +0.06%     
==========================================
  Files         266      266              
  Lines       16759    16801      +42     
==========================================
+ Hits         9345     9379      +34     
- Misses       6445     6448       +3     
- Partials      969      974       +5     

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