[wenwenwu999-maker]

Describe your change

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests?
• Documentation change?

Adds a solution for Project Euler problem 93.

The search merges pairs of numbers recursively instead of enumerating bracket
arrangements, and both orders of every pair are tried so the digits never need
permuting. All arithmetic uses fractions.Fraction to stay exact — with floats
the intermediate values drift to 23.999999999999996 and the answer is lost.

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.
• 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).