Add simple linear search algorithm

[AmeySGajare]

Description

Added a beginner-friendly implementation of the linear search algorithm in Python.
The implementation includes clear documentation, time and space complexity details, type hints, and example usage for better understanding.

Checklist

• I have read and followed the contributing guidelines
• This pull request is not a duplicate
• The algorithm is implemented from scratch
• The code follows the repository style
• 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".