Create flash_sort.py

[morgen-code]

This pull request adds an implementation of the Flash Sort algorithm in sorts/flash_sort.py.

Algorithm overview:
Flash Sort is a distribution-based sorting algorithm especially efficient for large datasets with elements that are uniformly distributed. Its main idea is to classify elements into buckets (classes) using a linear transformation, rearrange the array in-place using a cycle leader permutation, and finally apply insertion sort within each class for local ordering.

Implementation details:

• The number of classes (buckets) is empirically set to int(0.43 * n) (where n is the length of the array), following recommendations from the original paper and Wikipedia. This balance helps avoid both oversparse and overcrowded buckets.
• The implementation includes detailed comments and uses descriptive variable names for clarity.
• The function returns a new sorted list and does not modify the input array in-place.

Reference:

• Wikipedia: Flashsort

Use cases:
Most efficient when data is numeric and uniformly distributed. For other distributions, performance may degrade.

Closes #13203

Describe your change:

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

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• 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".