Fixed inconsistent typescript types between InterpolationAlgorithm and its implementations

[jfayot]

Description

Fixes inconsistent generated typescript types between InterpolationAlgorithm and its Hermite, Lagrange, and Linear implementations.

SampledPositionProperty.setInterpolationOptions expects an InterpolationAlgorithm, but the generated declarations did not correctly represent the implementations:

• type was not emitted when declared only within the namespace object literal.
• interpolate was emitted as required even though only Hermite supports it.

This PR:

• Declares each interpolation algorithm’s type property explicitly so it is included in generated declarations
• Adds a JSDoc @optional tag
• Marks InterpolationAlgorithm.interpolate as optional but preserves its API documentation
• Adds typetcript smoke tests covering Hermite, Lagrange, and Linear with SampledPositionProperty.setInterpolationOptions

The generated interface now correctly includes:

interpolate?(...): number[];

Issue number and link

Fixes: #13644

Testing plan

• run typescript definition generation and check the generated Cesium.d.ts
• run the non-webgl tests

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

AI acknowledgment

• I used AI to generate content in this PR
• If yes, I have reviewed the AI-generated content before submitting

[github-actions]

Thank you for the pull request, @jfayot!

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