Removed deprecated np.float_ calls

[SamuelBorden]

get_multi_local_extrema was calling np.float_ which is deprecated in numpy 2.0 and is causing BuildTheDocs to fail in other repos. I've replaced these calls with np.float64

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 60.51%. Comparing base (641e1cb) to head (a9dd693). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #80 +/- ## ======================================= Coverage 60.51% 60.51% ======================================= Files 48 48 Lines 3234 3234 ======================================= Hits 1957 1957 Misses 1277 1277 ```

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