Add fuzz target

[kevinbackhouse]

This resurrects #945 by @yevgenypats, which added a libFuzzer target. That commit doesn't seem to have been merged into the new main branch.

• I made some modifications to the fuzz target so that it also runs printStructure and writeMetadata
• I fixed some debug printfs that were spamming the logs
• I added an Action so that the fuzzer will be run for a short amount of time on every PR.

[codecov]

Codecov Report

Merging #1773 (e157fd6) into main (c7757d7) will increase coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1773      +/-   ##
==========================================
+ Coverage   67.29%   67.37%   +0.07%     
==========================================
  Files         151      151              
  Lines       20799    20807       +8     
==========================================
+ Hits        13997    14018      +21     
+ Misses       6802     6789      -13     

Impacted Files	Coverage Δ
src/iptc.cpp	76.05% <ø> (ø)
src/jpgimage.cpp	77.71% <ø> (+0.04%)	⬆️
src/tiffvisitor_int.cpp	87.51% <ø> (ø)
src/sonymn_int.cpp	88.88% <0.00%> (-0.59%)	⬇️
src/futils.cpp	87.34% <0.00%> (ø)
src/tags_int.cpp	87.20% <0.00%> (ø)
src/tags_int.hpp	90.90% <0.00%> (ø)
src/tiffimage_int.cpp	89.28% <0.00%> (ø)
src/bmffimage.cpp	81.36% <0.00%> (+0.05%)	⬆️
... and 1 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c7757d7...e157fd6. Read the comment docs.

[kevinbackhouse]

Not sure why the new action isn't showing up in the list of checks. I expect it will be shown there once the PR is merged. So I ran it on my own fork to make sure it's working: https://github.com/kevinbackhouse/exiv2/runs/3047928525