JP-3719: Fix names for intermediate spectral outlier detection files

[melanieclarke]

Resolves JP-3719

Closes #8734

For spectral modes with resampling, intermediate files from outlier detection are not being written correctly. There should be files written to the output directory with suffix 'outliers2d'. Instead, there are currently files written to the current directory with suffix 'outlieri2d', and some duplicate files written to the output directory with suffix 'outlier__outlier_s2d.fits'.

This PR should fix these issues by:

• removing the duplicate file saving mechanism in the spectral outlier detection method, in favor of the native one in the resampler
• modifying the resampling step to store the suffix 'i2d' for imaging and 's2d' for spectral data
• passing the output directory to the resampler in the spectral outlier detection interface.

I also added a unit test for spectral outlier detection, along with some checks for these kinds of regressions in intermediate file saving.

Checklist for PR authors (skip items if you don't have permissions or they are not applicable)

• [x] added entry in CHANGES.rst within the relevant release section
• [x] updated or added relevant tests
• [x] updated relevant documentation
• [x] added relevant milestone
• [x] added relevant label(s)
• [x] ran regression tests, post a link to the Jenkins job below. How to run regression tests on a PR
• [x] All comments are resolved
• [x] Make sure the JIRA ticket is resolved properly

[melanieclarke]

Regression tests here: https://github.com/spacetelescope/RegressionTests/actions/runs/10604279986

Failures are all unrelated.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 60.64%. Comparing base (f78361d) to head (e43af51). Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
jwst/outlier_detection/outlier_detection_step.py	0.00%	1 Missing :warning:
jwst/resample/resample.py	66.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #8735 +/- ## ========================================== + Coverage 60.55% 60.64% +0.08% ========================================== Files 372 372 Lines 38371 38371 ========================================== + Hits 23235 23269 +34 + Misses 15136 15102 -34 ```

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[melanieclarke]

Thanks for reviewing @emolter! Since this is a minor technical PR, I'll go ahead and merge when CI completes.