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

• [x] I have read and followed the contributing guidelines
• [x] This pull request is not a duplicate
• [x] The algorithm is implemented from scratch
• [x] The code follows the repository style
• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized.
• [x] I know that pull requests will not be merged if they fail the automated tests.
• [x] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• [x] All new Python files are placed inside an existing directory.
• [x] All filenames are in all lowercase characters with no spaces or dashes.
• [x] All functions and variable names follow Python naming conventions.
• [x] All function parameters and return values are annotated with Python type hints.
• [x] All functions have doctests that pass the automated testing.
• [x] All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• [x] 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".