Fix FuzzySet.union() constructor argument order

[HarshRajSinghania]

Describe your change:

Fixes #11871

FuzzySet.union() constructed the result as FuzzySet(name, min_left, max_right, avg_peak), but the constructor is (name, left_boundary, peak, right_boundary). Peak and right boundary were swapped, which is why the existing doctest reported the inconsistent peak=0.6, right_boundary=0.35.

This change passes the arguments in constructor order:

• left = min of the two left boundaries
• peak = average of the two peaks
• right = max of the two right boundaries

The class-level and method-level union doctests were updated to match the corrected construction. No other methods were changed.

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- required so the previously incorrect expected output matches the fixed constructor call
• 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 incorrect union method implementation in fuzzy operations #11871

Testing

python3 -m doctest -v fuzzy_logic/fuzzy_operations.py

Result: 22 passed, 0 failed.

[cclauss]

No files changed.