Refactor PolynomialPathFitter

[nickbianco]

Partially addresses issue #4291

Brief summary of changes

This change refactors PolynomialPathFitter to support future improvements as described in issue #4291.

• Moved the private helper function choose() to CommonUtilities.
• Remove all remaining private helper functions to an anonymous namespace in PolynomialPathFitter.cpp.
• Added the helper types CoordinateMap and Settings for passing configuration information to various parts of the path fitting pipeline.

Other minor changes include:

• Removed various instances of trailing whitespace in CommonUtilities.

Testing I've completed

Ran testPolynomialPathFitter.cpp.

Looking for feedback on...

CHANGELOG.md (choose one)

• no need to update because...internal refactor.

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This change is 

[Copilot]

Pull request overview

Refactors PolynomialPathFitter internals to make the path-fitting pipeline more modular and easier to evolve (per issue #4291), including moving shared helpers into CommonUtilities.

Changes:

• Adds a new public OpenSim::choose(n, k) utility in CommonUtilities.
• Moves PolynomialPathFitter pipeline helpers into an anonymous namespace and introduces internal Settings/CoordinateMap for configuration passing.
• Centralizes property validation into a new validateProperties() helper and updates data/model handling within run().

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 5 comments.

File	Description
OpenSim/Common/CommonUtilities.h	Declares new choose() utility and cleans up trailing whitespace.
OpenSim/Common/CommonUtilities.cpp	Defines choose() implementation.
OpenSim/Actuators/PolynomialPathFitter.h	Updates header guard, refactors private helpers, adds runtime members and validation hook.
OpenSim/Actuators/PolynomialPathFitter.cpp	Refactors pipeline into internal helpers with Settings passed through; adds validateProperties() and updates run() flow.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

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