Add closed_boundary argument to hamiltonians.models.TFIM

[renatomello]

Closes #433

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.51%. Comparing base (a0c9226) to head (585a2e7).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1791   +/-   ##
=======================================
  Coverage   99.51%   99.51%           
=======================================
  Files          79       79           
  Lines       13126    13142   +16     
=======================================
+ Hits        13062    13078   +16     
  Misses         64       64           

Flag	Coverage Δ
unittests	99.51% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 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.