FIX: Drop header before resampling image to avoid unsafe cast

[effigies]

int16 images with scale factors can get badly truncated or wrapped. This PR scales the data array and drops the header before passing to Affine().resample() to avoid this. We then re-add the dtype, though this may not be necessary. I think the effects of multiple interpolation are going to be minimal here, so keeping dtypes as expected is probably worth it.

[codecov[bot]]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (5ef205f) 76.62% compared to head (efa3528) 76.59%.

Files	Patch %	Lines
sdcflows/interfaces/utils.py	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #415 +/- ## ========================================== - Coverage 76.62% 76.59% -0.03% ========================================== Files 32 32 Lines 2823 2824 +1 Branches 373 373 ========================================== Hits 2163 2163 - Misses 594 595 +1 Partials 66 66 ``` | [Flag](https://app.codecov.io/gh/nipreps/sdcflows/pull/415/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipreps) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/nipreps/sdcflows/pull/415/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipreps) | `?` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipreps#carryforward-flags-in-the-pull-request-comment) to find out more.

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[effigies]

Not yet. Since that needs to work more broadly, a deeper review will be necessary.