[TheSmurfs]

Describe your change

• Fix a bug or typo in an existing algorithm?

Fixes #15635

Adler-32 is defined over a byte stream, but hashes/adler32.py summed
Unicode code points, so any non-ASCII input produced a checksum that no
standard implementation would produce (e.g. adler32('€100') returned
2211914046 instead of 196018850).

This PR iterates the UTF-8 encoded bytes instead of the characters, so the
result now matches the reference implementation zlib.adler32(text.encode())
for every input, and aligns with the sibling module hashes/crc32.py
(which already takes bytes and matches zlib.crc32).

Doctests added: the non-ASCII examples from the issue, plus a cross-check
against zlib.adler32. Also verified locally with 500 randomized inputs
(ASCII, Latin-1, CJK, emoji) against zlib — all match. ruff check and
ruff format --check pass.

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 hashes/adler32.py: checksum diverges from the Adler-32 spec for any non-ASCII input (sums Unicode code points instead of bytes) #15635".