Fix docs build: explicit JumpProcesses/StochasticDiffEq imports after DiffEq 8.0

[ChrisRackauckas-Claude]

Please ignore until reviewed by @ChrisRackauckas.

Summary

The Documentation workflow has been failing on master since 2026-05-11 (PR #591, the dependabot DifferentialEquations 7.11 -> 8.0 bump in docs/Project.toml).

DifferentialEquations.jl v8.0.0 only reexports SciMLBase and OrdinaryDiffEq. It no longer reexports JumpProcesses, StochasticDiffEq, DiffEqNoiseProcess, DiffEqCallbacks, etc. As a result, using DifferentialEquations in the tutorials no longer brings symbols like JumpProblem, ConstantRateJump, VariableRateJump, Direct, SSAStepper, or SRIW1 into scope, and the Documenter build fails with:

UndefVarError: `JumpProblem` not defined in `Main.__atexample__named__tut3`
@ docs/src/tutorials/jump_diffusion.md:163

The "also exported by ModelingToolkitBase / Catalyst" hints in Documenter's output are red herrings emitted because those packages are loaded elsewhere in the build — they do not actually shadow JumpProcesses.JumpProblem. The root cause is the lost reexport in DifferentialEquations 8.0.

Fix

Replace using DifferentialEquations with explicit imports in the two affected tutorial files:

• docs/src/tutorials/jump_diffusion.md (tut3): using JumpProcesses, StochasticDiffEq, OrdinaryDiffEq, Plots
• docs/src/tutorials/discrete_stochastic_example.md (tut2 @example and @setup blocks): using JumpProcesses, OrdinaryDiffEq, Plots, LinearAlgebra

Updated the corresponding Pkg.add prose to match. docs/src/tutorials/simple_poisson_process.md already uses explicit using JumpProcesses, Plots and was not affected.

Verification

Reproduced the failure locally against the current docs/Project.toml (DifferentialEquations 8.0.0, Catalyst 16.1.1, ModelingToolkitBase 1.35.0) on Julia 1.11:

julia> using DifferentialEquations
julia> isdefined(@__MODULE__, :JumpProblem)
false
julia> isdefined(@__MODULE__, :ConstantRateJump)
false
julia> isdefined(@__MODULE__, :SRIW1)
false

After the fix, ran the full code from both tutorials end-to-end with using JumpProcesses, StochasticDiffEq, OrdinaryDiffEq, Plots (for tut3) and using JumpProcesses, OrdinaryDiffEq, Plots, LinearAlgebra + using Catalyst (for tut2): both complete successfully.

Test plan

• CI's "Documentation" workflow goes green on this branch.

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