Improve BinarySearch documentation

[MD-Suhad]

• I have read [CONTRIBUTING.md](https://github.com/TheAlgorithms/Java/blob/master/CONTRIBUTING.md).
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new algorithms include a corresponding test class that validates their functionality.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

Closes #7327

This PR improves the BinarySearch documentation by adding:

• A step-by-step explanation of how binary search narrows the search space
• A simple input/output example
• Clear time complexity details

Tested locally with:
mvn -Dtest=BinarySearchTest test

Result:
Tests run: 8, Failures: 0, Errors: 0, Skipped: 0