docs/feat: improve shear stress logic with foundational physical principles

[definus6-dev]

Describe your change:

• 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.
• 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".

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Additional Context

This PR improves the shear_stress.py module by aligning the implementation with fundamental physical principles and Pythonic best practices.

• Refactored Interface: Replaced 0 as a placeholder with None.
• Enhanced Documentation: Added core mechanical context for better understanding.
• Robust Validation: Added non-negative checks and zero-division handling.

[algorithms-keeper]

Closing this pull request as invalid

@definus6-dev, this pull request is being closed as none of the checkboxes have been marked. It is important that you go through the checklist and mark the ones relevant to this pull request. Please read the Contributing guidelines.

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[definus6-dev]

Hello! I apologize for missing the mandatory checklist in my initial submission. I have now updated the PR description with the completed checklist. Could you please review and reopen this PR? Thank you!