fix: call complete on systems generated in MTKExt

[AayushSabharwal]

MTKv9 requires systems to be completed before creating XProblems

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

Add any other context about the problem here.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (4693404) 8.78% compared to head (90ccc2a) 8.62%.

Files	Patch %	Lines
ext/OptimizationMTKExt.jl	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #690      +/-   ##
=========================================
- Coverage    8.78%   8.62%   -0.16%     
=========================================
  Files          31      31              
  Lines        2515    2515              
=========================================
- Hits          221     217       -4     
- Misses       2294    2298       +4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.