Remove generic definitions of vectorplot! etc.

[j-fu]

They introduced dispatching ambiguities. Missing methods will throw an error anyway.

[Copilot]

Pull Request Overview

This PR removes the generic “missing implementation” fallback methods for various plot! functions—letting Julia’s dispatch automatically throw a MethodError—and tightens the vectorplot! signatures by explicitly typing the ptype parameter.

• Removed generic fallback definitions for gridplot!, scalarplot!, vectorplot!, and streamplot!
• Updated vectorplot! method signatures to require ptype::Type{T} with a where constraint

Comments suppressed due to low confidence (3)

src/dispatch.jl:722

• [nitpick] The parameter name ptype is ambiguous; consider renaming it to plotter_type for better readability and consistency.

function vectorplot!(ctx, ptype::Type{T}, ::Type{Val{1}}, grid, func::Matrix) where {T <: AbstractPlotterType}

src/dispatch.jl:725

• [nitpick] Similarly, rename ptype to plotter_type here to match the updated signature and improve clarity.

function vectorplot!(ctx, ptype::Type{T}, ::Type{Val{1}}, grid, func::Vector) where {T <: AbstractPlotterType}

src/dispatch.jl:410

• Since the generic fallback definitions were removed, add tests to verify that invoking gridplot!, scalarplot!, vectorplot!, and streamplot! without concrete implementations correctly raises a MethodError.

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