* fix: raise ValueError in encode() for non-lowercase input
encode() previously accepted uppercase letters, digits, and other
non-lowercase characters silently, producing incorrect/out-of-range
values (e.g. negative numbers for uppercase letters) instead of
failing. Add input validation using str.islower() and str.isalpha()
to raise a ValueError when the input isn't purely lowercase a-z.
Added a doctest covering the new error case.
* resolved doctest
* Fix Ruff 0.16 lint failures
* Enhance encode function error handling examples
Update error handling in encode function to include examples for mixed case and invalid characters.
* Fix indentation in test_cancer_data function
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
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Co-authored-by: Christian Clauss <cclauss@me.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
