Address Mypy Errors

[MattToast]

Mypy got smarter in later releases and started pointing out some potential type errors in SmartSim. This is a quick PR to address/suppress them.

Fixes #801

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.17%. Comparing base (d7d979e) to head (1a47a2b).
⚠️ Report is 26 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #798      +/-   ##
===========================================
- Coverage    83.91%   80.17%   -3.74%     
===========================================
  Files           83       78       -5     
  Lines         6284     6093     -191     
===========================================
- Hits          5273     4885     -388     
- Misses        1011     1208     +197     

Files with missing lines	Coverage Δ
smartsim/entity/model.py	96.04% <100.00%> (-0.04%)	⬇️

... and 41 files with indirect coverage changes

🚀 New features to boost your workflow:

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