Hey.
There is an option called syssolver that determines the strategy for solving Hypatia’s linear systems. The default is Solvers.QRCholDenseSystemSolver, so all the linear algebra is dense. You could try Solvers.SymIndefSparseSystemSolver{Float64}() if you suspecct that your problem will have sparse linear systems.
The files that you found do relate to the fact_cache field in the system solvers. But that’s a more subtle option. The HSL/Pardiso code probably hasn’t been used for a long time.