Satisfy MyPy 0.812 using __all__

[akaihola]

MyPy strict mode now disallows implicit re-export.
See fastapi/typer#112 (comment)

[sourcery-ai]

Sourcery Code Quality Report

✅  Merging this PR will increase code quality in the affected files by 0.09%.

Quality metrics	Before	After	Change
Complexity	1.39 ⭐	1.42 ⭐	0.03 👎
Method Length	70.06 🙂	70.89 🙂	0.83 👎
Working memory	10.12 😞	10.03 😞	-0.09 👍
Quality	69.99% 🙂	70.08% 🙂	0.09% 👍

Other metrics	Before	After	Change
Lines	502	509	7

Changed files	Quality Before	Quality After	Quality Change
src/darker/black_diff.py	80.41% ⭐	80.07% ⭐	-0.34% 👎
src/darker/command_line.py	63.84% 🙂	63.84% 🙂	0.00%
src/darker/import_sorting.py	73.70% 🙂	73.82% 🙂	0.12% 👍
src/darker/tests/test_main.py	67.07% 🙂	67.10% 🙂	0.03% 👍

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
src/darker/tests/test_main.py	test_main	0 ⭐	176 😞	23 ⛔	46.60% 😞	Try splitting into smaller methods. Extract out complex expressions
src/darker/command_line.py	make_argument_parser	3 ⭐	222 ⛔	9 🙂	55.94% 🙂	Try splitting into smaller methods
src/darker/tests/test_main.py	test_format_edited_parts	0 ⭐	122 😞	17 ⛔	56.15% 🙂	Try splitting into smaller methods. Extract out complex expressions
src/darker/tests/test_main.py	test_output_diff	0 ⭐	65 🙂	19 ⛔	62.51% 🙂	Extract out complex expressions
src/darker/import_sorting.py	apply_isort	3 ⭐	77 🙂	12 😞	65.68% 🙂	Extract out complex expressions

Legend and Explanation

The emojis denote the absolute quality of the code:

• ⭐ excellent
• 🙂 good
• 😞 poor
• ⛔ very poor

The 👍 and 👎 indicate whether the quality has improved or gotten worse with this pull request.

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Please see our documentation here for details on how these metrics are calculated.

We are actively working on this report - lots more documentation and extra metrics to come!

Let us know what you think of it by mentioning @sourcery-ai in a comment.