Add --find-renames and --find-copies to the diff command

[SandrineP]

Fix #88
Add --find-renames and --find-copies to the diff command

[codecov]

Codecov Report

❌ Patch coverage is 89.58333% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.60%. Comparing base (1ab489a) to head (9f38625).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/subcommand/diff_subcommand.cpp	89.58%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #115      +/-   ##
==========================================
- Coverage   87.52%   86.60%   -0.92%     
==========================================
  Files          60       60              
  Lines        2420     2463      +43     
  Branches      290      304      +14     
==========================================
+ Hits         2118     2133      +15     
- Misses        302      330      +28     

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[ianthomas23]

I've re-checked that both my and Johan's comments have been addressed, so let's merge.