MNT: Unpin tox, replace relative imports

[pllim]

Description

This pull request is to

• fix #171
• fix #152

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[codecov[bot]]

Codecov Report

Base: 84.88% // Head: 84.85% // Decreases project coverage by -0.03% :warning:

Coverage data is based on head (6f01f2d) compared to base (7a4f2da). Patch coverage: 94.28% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #173 +/- ## ========================================== - Coverage 84.88% 84.85% -0.04% ========================================== Files 13 13 Lines 1628 1637 +9 ========================================== + Hits 1382 1389 +7 - Misses 246 248 +2 ``` | [Impacted Files](https://codecov.io/gh/spacetelescope/stsynphot_refactor/pull/173?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope) | Coverage Δ | | |---|---|---| | [stsynphot/\_\_init\_\_.py](https://codecov.io/gh/spacetelescope/stsynphot_refactor/pull/173/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope#diff-c3RzeW5waG90L19faW5pdF9fLnB5) | `85.71% <80.00%> (-14.29%)` | :arrow_down: | | [stsynphot/catalog.py](https://codecov.io/gh/spacetelescope/stsynphot_refactor/pull/173/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope#diff-c3RzeW5waG90L2NhdGFsb2cucHk=) | `98.23% <100.00%> (ø)` | | | [stsynphot/commissioning/utils.py](https://codecov.io/gh/spacetelescope/stsynphot_refactor/pull/173/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope#diff-c3RzeW5waG90L2NvbW1pc3Npb25pbmcvdXRpbHMucHk=) | `29.82% <100.00%> (ø)` | | | [stsynphot/config.py](https://codecov.io/gh/spacetelescope/stsynphot_refactor/pull/173/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope#diff-c3RzeW5waG90L2NvbmZpZy5weQ==) | `98.11% <100.00%> (ø)` | | | [stsynphot/observationmode.py](https://codecov.io/gh/spacetelescope/stsynphot_refactor/pull/173/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope#diff-c3RzeW5waG90L29ic2VydmF0aW9ubW9kZS5weQ==) | `96.68% <100.00%> (ø)` | | | [stsynphot/spark.py](https://codecov.io/gh/spacetelescope/stsynphot_refactor/pull/173/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope#diff-c3RzeW5waG90L3NwYXJrLnB5) | `76.47% <100.00%> (ø)` | | | [stsynphot/spectrum.py](https://codecov.io/gh/spacetelescope/stsynphot_refactor/pull/173/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope#diff-c3RzeW5waG90L3NwZWN0cnVtLnB5) | `99.37% <100.00%> (ø)` | | | [stsynphot/spparser.py](https://codecov.io/gh/spacetelescope/stsynphot_refactor/pull/173/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope#diff-c3RzeW5waG90L3NwcGFyc2VyLnB5) | `89.31% <100.00%> (ø)` | | | [stsynphot/stio.py](https://codecov.io/gh/spacetelescope/stsynphot_refactor/pull/173/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope#diff-c3RzeW5waG90L3N0aW8ucHk=) | `96.35% <100.00%> (ø)` | | | [stsynphot/tables.py](https://codecov.io/gh/spacetelescope/stsynphot_refactor/pull/173/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope#diff-c3RzeW5waG90L3RhYmxlcy5weQ==) | `93.47% <100.00%> (ø)` | | | ... and [1 more](https://codecov.io/gh/spacetelescope/stsynphot_refactor/pull/173/diff?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope) | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope)

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