debug: do not fill unused decision variables in MovingHorizonEstimator after solve

[franckgaga]

This is a minor debug for clarity. Because of the hack of #207, the returned solution will sometimes include 1.0 values for the unused decision variables (when the windows are not filled, and it depends of the optimizer). This PR fills the estim.Z̃ vector after solution with only the used variable. The unused variables will be left at their initialized value, which is 0.0. If the user want to inspect estim.Z̃ for some reasons, 0.0 values is less troubling than 1.0 values.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.71%. Comparing base (d2c359c) to head (6467eea).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #400      +/-   ##
==========================================
- Coverage   98.71%   98.71%   -0.01%     
==========================================
  Files          27       27              
  Lines        5691     5686       -5     
==========================================
- Hits         5618     5613       -5     
  Misses         73       73              

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.