feat: exploit_mitigations: better error handling and feedback

[jstucke]

The exploit_mitigation plugin is in some rare cases called on files that aren't actually ELF files. This PR adds better error handling and user feedback,

[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.23810% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.48%. Comparing base (a8d0625) to head (e1cf203).

Files with missing lines	Patch %	Lines
...is/exploit_mitigations/code/exploit_mitigations.py	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1479      +/-   ##
==========================================
+ Coverage   92.40%   92.48%   +0.08%     
==========================================
  Files         370      370              
  Lines       20851    20826      -25     
==========================================
- Hits        19267    19261       -6     
+ Misses       1584     1565      -19     

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