TLC for fuzzy_logic/: restore disabled demo dependency-free + add README

[priya-sundaram-dev]

Describe your change:

TLC pass on fuzzy_logic/ — the first directory from the shortlist in #15081 (last new contribution 2024-09, 2 files, no README). Starting here since it has the same "restore a disabled file + add tests/README/URLs" shape as the audio_filters/ exercise (#15087).

What this does:

• Restores fuzzy_operations.py.DISABLED.txt dependency-free. It was disabled because it imported the third-party scikit-fuzzy (import skfuzzy). I rewrote it as fuzzy_set_operations.py using NumPy only (already in pyproject.toml). It implements the classic Zadeh operators on sampled membership vectors — union, intersection, complement, difference, algebraic sum/product, bounded sum/difference — plus a triangular_membership helper.
• Adds doctests to every function instead of the old __main__-only matplotlib demo. The __main__ block still reproduces the original "young vs. middle-aged" figure and degrades gracefully (prints a summary) when matplotlib isn't installed.
• Adds fuzzy_logic/README.md covering both modules, with Wikipedia links and a runnable example, and explaining how the two files complement each other (fuzzy_operations.py keeps the parametric triangular representation; fuzzy_set_operations.py works on arbitrary sampled membership shapes).
• Removes the obsolete .DISABLED.txt now that its intent lives in a working, tested module.

Credit kept to Jigyasa Gandhi (original scikit-fuzzy demo) and @Shreya123714 (the FuzzySet class).

Verified locally: pytest --doctest-modules fuzzy_logic/ (15 passed), ruff check, ruff format --check all pass.

Relates to #15081.

• 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.

[algorithms-keeper]

Click here to look at the relevant links ⬇️

🔗 Relevant Links

Repository:

• Contributing guidelines
• Project Euler solution guidelines

Python:

• Formatted string literals (f-strings)
• Type hints
• doctest
• unittest
• pytest

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[cclauss]

I agree with @algorithms-keeper that single-letter names for function parameters are not self-documenting for the caller.

[priya-sundaram-dev]

Done — pushed in bbef392:

• Descriptive parameter names (agreeing with @algorithms-keeper and @cclauss): x → grid, the two operands → membership_a/membership_b, and fuzzy_complement's single operand → membership. Doctests call positionally so results are unchanged; all still pass.
• Dropped from __future__ import annotations — not needed in a Python 3.14t-only repo.

ruff and pre-commit.ci are green; the NDArray[np.float64] hints evaluate fine at runtime without the future import. Thanks for the review!