Add exponential_search doctest for empty array edge case

[vivekkumarrathour]

This doctest demonstrates that exponential_search correctly handles empty arrays by returning -1.

Describe your change:

• 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.
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• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
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[Copilot]

🟡 Changes recommended

The new doctest is mis-indented and, once corrected, currently fails because exponential_search([] , ...) raises IndexError instead of returning -1.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This pull request aims to add a doctest demonstrating how exponential_search behaves on an empty input collection.

Changes:

• Adds a new doctest example for the empty-collection edge case in exponential_search.

File summaries

File	Description
searches/exponential_search.py	Adds a doctest intended to validate empty-input behavior for exponential_search.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Lite

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