Raise ModelingToolkitBase DiffEqBase floor for symbolic diagnostics

Update the DiffEqBase compatibility entry in lib/ModelingToolkitBase/Project.toml, starting from its current 7.4.2 floor. Reproduce the incompatible SciMLBase 3.44.0 and DiffEqBase 7.10.0 pair if needed, then rerun the ModelingToolkitBase downgrade CI job. Done means the floor is 7.12 and the downgrade job no longer fails with the missing symbolic_diagnostic field.

ModelingToolkitBase downgrade CI resolves an incompatible pair on clean ModelingToolkit master d7f3ad523c00b4150281f259d1e97618fba79982: SciMLBase 3.44.0 and DiffEqBase 7.10.0. This is unrelated to the one-line change in https://github.com/SciML/ModelingToolkit.jl/pull/4920.

Failing job: https://github.com/SciML/ModelingToolkit.jl/actions/runs/31368626108/job/93392420550

Observed CI failure:

InitializationSystem Test: Error During Test
LoadError: type DEVerbosity has no field symbolic_diagnostic
@ SciMLBase .../integrator_interface.jl:1012

Exact clean standalone reproduction on Julia 1.10.11:

julialauncher +1.10 -e "using Pkg; Pkg.activate(\"base-min-repro-env\"); Pkg.add([PackageSpec(name=\"SciMLBase\", version=\"3.44.0\"), PackageSpec(name=\"DiffEqBase\", version=\"7.10.0\")]); using SciMLBase, DiffEqBase; verbose = DEVerbosity(); @show hasproperty(verbose, :symbolic_diagnostic); verbose.symbolic_diagnostic"

Observed result:

hasproperty(verbose, :symbolic_diagnostic) = false
type DEVerbosity has no field symbolic_diagnostic

Changing only DiffEqBase to 7.12.0 reports:

hasproperty(verbose, :symbolic_diagnostic) = true
verbose.symbolic_diagnostic = SciMLLogging.MessageLevel(3)

The symbolic_diagnostic field was added by OrdinaryDiffEq commit 0237ef1552 in https://github.com/SciML/OrdinaryDiffEq.jl/pull/3731. The code still declared DiffEqBase 7.11.0 at that commit and was first shipped by the following version bump as DiffEqBase 7.12.0.

ModelingToolkitBase currently permits DiffEqBase 7.4.2 in lib/ModelingToolkitBase/Project.toml. The focused resolution is to raise that compatibility floor to 7.12 and rerun the ModelingToolkitBase downgrade job. This should be a standalone mechanical compatibility PR.