[Issue 1310] Switch type hint for lambdas to list[float]

[IAlibay]

Fixes #1310

In the ABFE protocol we actually use npt.NDArray, but the openmmtools code wants list, so we should use that instead.

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[github-actions]

No API break detected ✅

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.65%. Comparing base (a7d7c72) to head (6b94931).
⚠️ Report is 251 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1341      +/-   ##
==========================================
- Coverage   94.66%   92.65%   -2.02%     
==========================================
  Files         143      143              
  Lines       10994    10994              
==========================================
- Hits        10408    10186     -222     
- Misses        586      808     +222     

Flag	Coverage Δ
fast-tests	92.65% <ø> (?)
slow-tests	?

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