Add copy method to cstruct instance

[Schamper]

Closes #79

[codecov]

Codecov Report

❌ Patch coverage is 0% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (9f12b1e) to head (cc3738b).

Files with missing lines	Patch %	Lines
dissect/cstruct/cstruct.py	0.00%	18 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #140   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files         21      21           
  Lines       2482    2500   +18     
=====================================
- Misses      2482    2500   +18     

Flag	Coverage Δ
unittests	0.00% <0.00%> (ø)

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[codspeed-hq]

Merging this PR will not alter performance

✅ 12 untouched benchmarks

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_{Comparing add-copy (cc3738b) with main (9f12b1e)}