Add virtual destructors to StateVector classes

[mlxd]

Context: Fixes #188

Description of the Change: Add virtual destructors to StateVector and derived types.

Benefits: Prevents issues with destructor order calls.

Possible Drawbacks: None.

Related GitHub Issues: #188

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit .github/CHANGELOG.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
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[codecov]

Codecov Report

Merging #200 (944742b) into master (978f739) will not change coverage.
The diff coverage is n/a.

❗ Current head 944742b differs from pull request most recent head 26d6f80. Consider uploading reports for the commit 26d6f80 to get more accurate results

@@           Coverage Diff           @@
##           master     #200   +/-   ##
=======================================
  Coverage   99.64%   99.64%           
=======================================
  Files           4        4           
  Lines         278      278           
=======================================
  Hits          277      277           
  Misses          1        1           

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[github-actions]

Test Report (C++) on Ubuntu

       1 files  ±0         1 suites  ±0   0s ⏱️ ±0s
   378 tests ±0     378 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
2 233 runs  ±0  2 233 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 26d6f80. ± Comparison against base commit 978f739.

♻️ This comment has been updated with latest results.

[AmintorDusko]

Short and Sweet!