Minor additions + bug-fixes to get Pydra/Arcana tests to pass

[tclose]

• Better handling in actual_ext for case where file extensions are None
• Allow new_stem when copying a single file
• WithMagicVersion mixin class
• Array conversion from tuple-style string

[codecov[bot]]

Codecov Report

Patch coverage: 57.50% and project coverage change: -0.31% :warning:

Comparison is base (6833d2b) 93.23% compared to head (5cc078f) 92.93%. Report is 2 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #32 +/- ## ========================================== - Coverage 93.23% 92.93% -0.31% ========================================== Files 30 30 Lines 4275 4304 +29 Branches 421 431 +10 ========================================== + Hits 3986 4000 +14 - Misses 221 236 +15 Partials 68 68 ``` | [Files Changed](https://app.codecov.io/gh/ArcanaFramework/fileformats/pull/32?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ArcanaFramework) | Coverage Δ | | |---|---|---| | [fileformats/core/mixin.py](https://app.codecov.io/gh/ArcanaFramework/fileformats/pull/32?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ArcanaFramework#diff-ZmlsZWZvcm1hdHMvY29yZS9taXhpbi5weQ==) | `78.40% <47.61%> (-2.91%)` | :arrow_down: | | [fileformats/field/\_\_init\_\_.py](https://app.codecov.io/gh/ArcanaFramework/fileformats/pull/32?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ArcanaFramework#diff-ZmlsZWZvcm1hdHMvZmllbGQvX19pbml0X18ucHk=) | `85.71% <50.00%> (ø)` | | | [fileformats/core/fileset.py](https://app.codecov.io/gh/ArcanaFramework/fileformats/pull/32?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ArcanaFramework#diff-ZmlsZWZvcm1hdHMvY29yZS9maWxlc2V0LnB5) | `85.15% <66.66%> (-0.57%)` | :arrow_down: | | [fileformats/generic/\_\_init\_\_.py](https://app.codecov.io/gh/ArcanaFramework/fileformats/pull/32?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ArcanaFramework#diff-ZmlsZWZvcm1hdHMvZ2VuZXJpYy9fX2luaXRfXy5weQ==) | `73.85% <75.00%> (+0.17%)` | :arrow_up: | | [fileformats/core/exceptions.py](https://app.codecov.io/gh/ArcanaFramework/fileformats/pull/32?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ArcanaFramework#diff-ZmlsZWZvcm1hdHMvY29yZS9leGNlcHRpb25zLnB5) | `100.00% <100.00%> (ø)` | |

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