Add unit tests for the cylindrical shell rolling engine

[YurMil]

YurMil/Shell-Rolling-Master computes developed lengths from a normative basis (neutral-axis/K-factor treatment, EN and ASME presets) and has no tests at all — the only calculator in the catalog without them.

This is the engine behind the worked example published in #118, where the numbers were verified by running calculateShell manually. Those same cases should be committed as tests.

Suggested starting coverage:

• cylinder developed length from OD and from ID (the ID/OD distinction is worth a test of its own — it is a +94 mm error at DN 2000)
• K-factor effect at the range limits
• cone and eccentric-cone modes
• validation guards: K outside 0..1, gap larger than the circumference, non-positive dimensions

Acceptance criteria:

• Vitest suite with reference cases computed from the standard relations
• Tests run in CI on pull requests and before deploy
• Fixtures published as validation cases on the docs page, as with the other calculators

Found while writing the QA strategy page (#105).

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