Add Armstrong number check algorithm

[Pranav-MSK]

Implement function to check Armstrong numbers with examples.

Describe your change:

This adds a function to check if a given integer is an Armstrong number (also known as a narcissistic number). The function works for all non-negative integers and correctly handles edge cases like 0 and 1. Negative numbers are not considered Armstrong numbers.
The algorithm iterates over the digits of the number, raises each digit to the power of the number of digits, and sums them to check if the sum equals the original number.

It includes:

• Type hints for input and output
• Clear docstrings with examples and edge cases
• Doctests that pass all tests
• No external libraries used
• Follows PEP8 naming conventions

• 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".