Adds FileSet.move method

[tclose]

• Adds FileSet.move method, including refactoring of FileSet.copy to split into smaller sub-methods
• Handles forward refs in mime type conversion

[codecov[bot]]

Codecov Report

Attention: 30 lines in your changes are missing coverage. Please review.

Comparison is base (c622f2a) 93.70% compared to head (30d6f0a) 93.52%.

Files	Patch %	Lines
fileformats/core/fileset.py	78.08%	10 Missing and 6 partials :warning:
fileformats/core/utils.py	22.22%	5 Missing and 2 partials :warning:
fileformats/core/mixin.py	33.33%	6 Missing :warning:
fileformats/core/converter.py	88.88%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #54 +/- ## ========================================== - Coverage 93.70% 93.52% -0.18% ========================================== Files 37 37 Lines 4624 4681 +57 Branches 503 516 +13 ========================================== + Hits 4333 4378 +45 - Misses 214 220 +6 - Partials 77 83 +6 ```

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