Add optional callback performed before step to gsDynamicBase.h

[mhodzelmans]

I have some boundary DOFs with prescribed velocities. Every Newmark timestep, I needed to compute consistens accelerations/positions, and resulting internal forces. This change enables that by making it possible to inject a callback.

Also, a #pragma once was missing.

[hverhelst]

Thanks! Small change (did not compile it) for clarity

[Copilot]

Pull request overview

Enables users of gsDynamicBase time integrators (e.g., Newmark) to run custom logic immediately before each non-const timestep, supporting workflows like enforcing prescribed boundary velocities and recomputing consistent states.

Changes:

• Added a configurable pre-step callback API to gsDynamicBase and invoked it at the start of step(T dt).
• Ensured m_status is updated with the result of _step(...) in step(T dt).
• Added missing #pragma once to gsStructuralAnalysisTypes.h.

Reviewed changes

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

File	Description
src/gsStructuralAnalysisTools/gsStructuralAnalysisTypes.h	Adds #pragma once to avoid multiple-inclusion issues.
src/gsDynamicSolvers/gsDynamicBase.h	Adds pre-step callback support and updates step status bookkeeping.

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