Fixes for interpolating vector valued functions

[codecov-commenter]

Codecov Report

Merging #13 (777f49c) into main (4160329) will increase coverage by 0.95%. The diff coverage is 100.00%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #13 +/- ## ========================================== + Coverage 96.83% 97.78% +0.95% ========================================== Files 4 4 Lines 631 633 +2 ========================================== + Hits 611 619 +8 + Misses 20 14 -6 ``` | [Files](https://app.codecov.io/gh/f0uriest/interpax/pull/13?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Rory+Conlin) | Coverage Δ | | |---|---|---| | [interpax/\_spline.py](https://app.codecov.io/gh/f0uriest/interpax/pull/13?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Rory+Conlin#diff-aW50ZXJwYXgvX3NwbGluZS5weQ==) | `98.08% <100.00%> (+1.05%)` | :arrow_up: |