Add bssfp signal model

[JeffFessler]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.87%. Comparing base (489ffe4) to head (d2fc1dc).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #47      +/-   ##
==========================================
+ Coverage   99.62%   99.87%   +0.25%     
==========================================
  Files           9       10       +1     
  Lines        1583     1644      +61     
==========================================
+ Hits         1577     1642      +65     
+ Misses          6        2       -4     

☔ 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.