✅ Add doctests to string conversion functions

[Nitin-Prata]

Describe your change:

Contributes to #9943
Closes #13601

• Added doctests for compute_transform_tables and assemble_transformation
• Covered edge cases like empty strings and common transformations
• Verified all doctests pass via python -m doctest -v

• 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.
• 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".

[Nitin-Prata]

Hi,
This PR adds doctests to string_conversion.py and all checks have passed.
It’s been reviewed and approved by two contributors.
Could someone with write access please review or merge it?

[Copilot]

🟡 Changes recommended

The PR description must mark the doctest change option to avoid automatic closure.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Adds and refines doctests for string conversion functions without changing runtime behavior.

Changes:

• Adds an empty-string doctest.
• Simplifies transformation examples.
• Corrects docstring wording.

File summaries

File	Description
strings/min_cost_string_conversion.py	Updates doctest examples and documentation.

Review note: Select “Add or change doctests?” in the pull request description.

Review details

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

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