Add fibonacci algorithm in maths folder

[akrutitiwari24]

Describe your change:

• Add an algorithm

This PR adds the Fibonacci sequence algorithm in the maths/ folder.
The function fibonacci(n: int) -> list[int] returns the first n numbers of the Fibonacci sequence.
It includes proper type hints, follows Python naming conventions, and contains doctests to verify correct behavior.

Reference: Fibonacci sequence - Wikipedia

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.