fix(expr): Coerce arguments to min/max to numbers

[effigies]

max(events.columns.onset) was always null, because the column contains strings. Here we coerce values to numbers and filter nans, which gives us the behavior we want.

[codecov[bot]]

Codecov Report

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

Project coverage is 87.12%. Comparing base (5de6cdd) to head (6f3b82d).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2038 +/- ## ========================================== + Coverage 85.75% 87.12% +1.37% ========================================== Files 91 136 +45 Lines 3785 6449 +2664 Branches 1218 1551 +333 ========================================== + Hits 3246 5619 +2373 - Misses 453 740 +287 - Partials 86 90 +4 ```

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