Fix MakieExt and ControlPlotsExt define VortexStepMethod.plot_geometry for the same type

[ufechner7]

Fixes #236

[Copilot]

Pull request overview

This PR resolves the method redefinition/precompilation conflict when both Makie and ControlPlots are loaded by introducing an explicit plotting-backend dispatch layer in VortexStepMethod.plot_* APIs (Fixes #236).

Changes:

• Added PlotBackend dispatch types plus set_plot_backend! and wrapper methods that route plotting calls through an active backend.
• Updated Makie and ControlPlots extensions to implement plotting methods with an additional backend-dispatch argument.
• Initialized a default active backend from each extension on load.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
src/VortexStepMethod.jl	Introduces backend dispatch types, backend selection state, and wrapper routing for plotting entry points.
ext/VortexStepMethodMakieExt.jl	Moves Makie plotting methods onto backend-dispatched signatures and sets Makie as the default backend on extension init.
ext/VortexStepMethodControlPlotsExt.jl	Moves ControlPlots plotting methods onto backend-dispatched signatures and sets ControlPlots as the default backend on extension init.

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[codecov]

Codecov Report

❌ Patch coverage is 89.28571% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
ext/VortexStepMethodControlPlotsExt.jl	40.00%	3 Missing ⚠️

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