Resolve sublibrary downgrade failures behind the old #417 disable (now re-enabled)

Drop vec/flatten/unflatten roundtrips in MIRK/FIRK/MIRKN nlprob construction

MIRK 1.15+ adaptive mesh refinement: UndefRefError on nonlinear BVPs

Collocation BVP solvers overwrite input for initial guess

BoundaryValueDiffEq fails to compile when DataStructures held back <0.19 by other package in Project

Possible type instability in `BVP.BVProblem()` and `BVP.solve()`

Differences between the interpolation between the solution and the intermediarry `EvalSol`

Imported binding OptimizationBase.OptimizationVerbosity was undeclared at import time during import to BoundaryValueDiffEqCore.

Use SciMLLogging for warnings and log messages

BVPSOL test errors: Cannot find method(s) for bvpsol