trapezoidal fuzzy set

[Shreya123714]

Describe your change:

I created a trapezoidal fuzzy set, which will be further used in a fuzzy inference system. I plan to add the algorithm for the fuzzy inference system in another PR.

• [X] 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:

• [X] I have read CONTRIBUTING.md.
• [X] This pull request is all my own work -- I have not plagiarized.
• [X] I know that pull requests will not be merged if they fail the automated tests.
• [X] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• [X] All new Python files are placed inside an existing directory.
• [X] All filenames are in all lowercase characters with no spaces or dashes.
• [X] All functions and variable names follow Python naming conventions.
• [X] All function parameters and return values are annotated with Python type hints.
• [X] All functions have doctests that pass the automated testing.
• [X] All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• [X] If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".

[Shreya123714]

hey @cclauss could you please take a look at my PR when you have a moment? I appreciate your feedback 🙂🙏🙏🙌

[cclauss]

Closing require_tests PRs to prepare for Hacktoberfest