Create flash sort

[cemmanuelsr]

Describe your change:

• [x] Add an algorithm?
• [ ] Fix a bug or typo in an existing algorithm?
• [x] Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• [ ] Documentation change?

Checklist:

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized.
• [x] I know that pull requests will not be merged if they fail the automated tests.
• [x] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• [x] All new Python files are placed inside an existing directory.
• [x] All filenames are in all lowercase characters with no spaces or dashes.
• [x] All functions and variable names follow Python naming conventions.
• [x] All function parameters and return values are annotated with Python type hints.
• [x] All functions have doctests that pass the automated testing.
• [x] All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• [x] If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".

[cclauss]

mypy.....................................................................Failed

• hook id: mypy
• exit code: 1

sorts/flash_sort.py:58: error: Value of type "Iterable[Any]" is not indexable  [index]
sorts/flash_sort.py:59: error: Value of type "Iterable[Any]" is not indexable  [index]
sorts/flash_sort.py:76: error: Value of type "Iterable[Any]" is not indexable  [index]
sorts/flash_sort.py:78: error: Argument 1 to "swap_index" has incompatible type "float"; expected "int"  [arg-type]
sorts/flash_sort.py:79: error: Unsupported target for indexed assignment ("Iterable[Any]")  [index]
sorts/flash_sort.py:79: error: Value of type "Iterable[Any]" is not indexable  [index]
sorts/flash_sort.py:80: error: Value of type "Iterable[Any]" is not indexable  [index]
sorts/flash_sort.py:96: error: Argument 1 to "len" has incompatible type "Iterable[Any]"; expected "Sized"  [arg-type]
sorts/flash_sort.py:97: error: Value of type "Iterable[Any]" is not indexable  [index]
sorts/flash_sort.py:100: error: Value of type "Iterable[Any]" is not indexable  [index]
sorts/flash_sort.py:101: error: Unsupported target for indexed assignment ("Iterable[Any]")  [index]
sorts/flash_sort.py:101: error: Value of type "Iterable[Any]" is not indexable  [index]
sorts/flash_sort.py:104: error: Unsupported target for indexed assignment ("Iterable[Any]")  [index]
sorts/flash_sort.py:123: error: Argument 1 to "len" has incompatible type "Iterable[Any]"; expected "Sized"  [arg-type]
sorts/flash_sort.py:127: error: Value of type "Iterable[Any]" is not indexable  [index]
sorts/flash_sort.py:129: error: Value of type "Iterable[Any]" is not indexable  [index]
sorts/flash_sort.py:130: error: Value of type "Iterable[Any]" is not indexable  [index]
sorts/flash_sort.py:131: error: Value of type "Iterable[Any]" is not indexable  [index]
sorts/flash_sort.py:132: error: Value of type "Iterable[Any]" is not indexable  [index]
sorts/flash_sort.py:135: error: Return value expected  [return-value]
sorts/flash_sort.py:140: error: No overload variant of "__getitem__" of "list" matches argument type "float"  [call-overload]
sorts/flash_sort.py:140: note: Possible overload variants:
sorts/flash_sort.py:140: note:     def __getitem__(self, SupportsIndex, /) -> int
sorts/flash_sort.py:140: note:     def __getitem__(self, slice, /) -> list[int]
sorts/flash_sort.py:140: error: No overload variant of "__setitem__" of "list" matches argument types "float", "Any"  [call-overload]
sorts/flash_sort.py:140: note:     def __setitem__(self, SupportsIndex, int, /) -> None
sorts/flash_sort.py:140: note:     def __setitem__(self, slice, Iterable[int], /) -> None
sorts/flash_sort.py:155: error: Unsupported target for indexed assignment ("Iterable[Any]")  [index]
sorts/flash_sort.py:155: error: Value of type "Iterable[Any]" is not indexable  [index]
sorts/flash_sort.py:157: error: Unsupported target for indexed assignment ("Iterable[Any]")  [index]
sorts/flash_sort.py:157: error: Value of type "Iterable[Any]" is not indexable  [index]
Found 26 errors in 1 file (checked 1288 source files)