feat: add mypy support and type stubs

[eonu]

Add mypy support and type stubs

• Add mypy support and type stubs.

Checklist

• I have added new tests (if necessary).
• I have ensured that tests and coverage are passing on CI.
• I have updated any relevant documentation (if necessary).
• I have used a descriptive pull request title.

[coveralls]

Pull Request Test Coverage Report for Build f7f1a43a-5e1c-4bd2-ac6a-ea2564efaf96

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 72 unchanged lines in 9 files lost coverage.
• Overall coverage decreased (-0.9%) to 91.017%

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Files with Coverage Reduction	New Missed Lines	%
core/group.py	1	98.48%
_internal/_metaclass.py	1	97.92%
_internal/_group.py	2	87.5%
core/init.py	4	80.49%
decorators.py	5	93.51%
_internal/_decorators.py	6	85.0%
_internal/_command.py	10	93.41%
_internal/_types/click.py	12	94.17%
_internal/_sections.py	31	18.37%

Totals
Change from base Build 03bd8cac-9fb2-43ae-8628-f50b253e3fce:	-0.9%
Covered Lines:	1074
Relevant Lines:	1180

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💛 - Coveralls