Add catalan number

[DivyanshRajSoni]

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".

Implementation: Added maths/catalan_number.py with three different approaches:

• Dynamic programming (O(n²))
• Recursive with memoization (O(n²))
• Binomial coefficient formula (O(n))

Testing: 18 passing doctests covering valid inputs and error cases

Reference: https://en.wikipedia.org/wiki/Catalan_number

[DivyanshRajSoni]

Please Sir , Merge it ...

[Tarannum9623]

Hi! Can you help me by telling why my build test is failing, I want to contribute search_in_a_rotated_sorted_array in search directory and my build test failed.
PR: Search in rotated sorted array #13245