Add unit tests for least-covered Python modules + pytest CI

[devin-ai-integration]

Summary

The repo has 126 Python modules and effectively 0% test coverage (the only pre-existing test files were a default CRA App.test.js and a stray Java Test.java). This PR bootstraps a Python test suite and CI.

Since the projects are standalone scripts in directories with spaces (not importable packages), tests/conftest.py adds a load_module(relative_path, name) helper that loads any script by path via importlib. I targeted the modules with clean, deterministic, side-effect-free logic (guarded by if __name__ == "__main__"), which are the highest-value/lowest-risk to lock down first.

50 tests added across 7 previously-untested modules:

• Scytale Cipher/cipher.py — encrypt/decrypt, round-trips, key=1 identity, trailing-partial-row drop
• morse_translator/morse_translator.py — encode/decode round-trips, digit table, KeyError on lowercase input
• url_shortener/url_shortener.py — md5-prefix short URLs, caching, expand + not-found path
• Sentiment_analyzer_for_prototypes/sentiment_analyzer.py — clean_text, positive/negative/neutral scoring, word frequency, ASCII cloud
• Color Palette Generator/main.py — palette length, hex-format validation
• Hash/hashing.py — calculate_hash vs hashlib for md5/sha1/sha256/sha512, empty/large files, SystemExit on missing file
• password_generator/password_generator.py — length bounds, per-charset selection, no-option error path

Tests assert the code's actual behavior (verified by running each function), so they document real behavior rather than forcing a spec.

Also added:

• pytest.ini (testpaths=tests), requirements-test.txt (pytest pinned)
• .github/workflows/python-tests.yml — runs pytest on push/PR touching Python files
• .gitignore entries for __pycache__/, *.pyc, .pytest_cache/

Run locally:

pip install -r requirements-test.txt && python -m pytest -q
# 50 passed

Link to Devin session: https://app.devin.ai/sessions/e358d5f9691749f781c2b91ff99ee7fa
Requested by: @josharsh

[devin-ai-integration]

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