Refactor visualization interface: optional Plots, uniform API

[BatyLeo]

• Plots.jl is now a weak dependency, through a package extension
• plot_data is removed. The interface is now:
  • has_visualization(bench): runtime check (true for Argmax2D, Warcraft, SVS, DVS)
  • plot_instance(bench, sample; kwargs...)
  • plot_solution(bench, sample; kwargs...) / plot_solution(bench, sample, y; kwargs)
  • plot_trajectory(bench, traj; kwargs...): dynamic benchmarks; grid of per-epoch subplots
  • animate_trajectory(bench, traj; fps=1): dynamic benchmarks; returns a Plots.Animation
• All four plot extensions (argmax2d_plots.jl, warcraft_plots.jl, svs_plots.jl, dvs_plots.jl) implement the new interface.
• Docs updated

[codecov]

Codecov Report

❌ Patch coverage is 95.38462% with 12 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
ext/plots/dvs_plots.jl	93.58%	10 Missing ⚠️
ext/plots/svs_plots.jl	97.61%	1 Missing ⚠️
src/Utils/interface.jl	0.00%	1 Missing ⚠️

Files with missing lines	Coverage Δ
ext/DFLBenchmarksPlotsExt.jl	100.00% <100.00%> (ø)
ext/plots/argmax2d_plots.jl	100.00% <100.00%> (ø)
ext/plots/warcraft_plots.jl	100.00% <100.00%> (ø)
src/Argmax2D/Argmax2D.jl	100.00% <ø> (ø)
src/Argmax2D/polytope.jl	100.00% <ø> (ø)
src/DecisionFocusedLearningBenchmarks.jl	100.00% <ø> (ø)
...namicVehicleScheduling/DynamicVehicleScheduling.jl	100.00% <ø> (ø)
src/DynamicVehicleScheduling/plot_data.jl	100.00% <100.00%> (ø)
...icVehicleScheduling/StochasticVehicleScheduling.jl	100.00% <ø> (ø)
src/Utils/Utils.jl	100.00% <ø> (ø)
... and 4 more

... and 2 files with indirect coverage changes

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