refactor: restructure fuzzer

[yashugarg]

This PR revamps the current file structure of the fuzz module,
It also includes changes in generated protobuf files allowing all files to run similarly with:
python -m fuzz.fuzz_foo

[codecov-commenter]

Codecov Report

Merging #1906 (4effa0e) into main (64c1393) will decrease coverage by 2.25%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1906      +/-   ##
==========================================
- Coverage   89.64%   87.39%   -2.26%     
==========================================
  Files         316      316              
  Lines        7226     7226              
  Branches     1176     1176              
==========================================
- Hits         6478     6315     -163     
- Misses        484      646     +162     
- Partials      264      265       +1     

Flag	Coverage Δ
longtests	78.84% <ø> (+0.01%)	⬆️
win-longtests	86.34% <ø> (-2.30%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cve_bin_tool/nvd_api.py	24.00% <0.00%> (-52.80%)	⬇️
test/test_nvd_api.py	50.87% <0.00%> (-40.36%)	⬇️
cve_bin_tool/data_sources/osv_source.py	63.63% <0.00%> (-26.74%)	⬇️
cve_bin_tool/cvedb.py	78.15% <0.00%> (-8.54%)	⬇️
cve_bin_tool/cli.py	77.03% <0.00%> (+0.37%)	⬆️

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[terriko]

This looks like a nice way to restructure stuff. We could still use some more instructions in the fuzz/readme.md file (even if it's just a few lines saying "run python -m fuzz.$option and the list of options is in the directory"), but those can happen in a separate PR.