[BUG] ARKodeSetDefaults Memory Leaks and Inconsistencies

[Steven-Roberts]

Current Behavior:

When ARKodeSetDefaults is called, some of the implementations NULL out Butcher tables and the nonlinear solver without freeing:

sundials/src/arkode/arkode_arkstep_io.c

Lines 680 to 682 in c28eaa3

	step_mem->Be = NULL; /* no Butcher tables */
	step_mem->Bi = NULL;
	step_mem->NLS = NULL; /* no nonlinear solver object */

sundials/src/arkode/arkode_erkstep_io.c

Line 310 in c28eaa3

step_mem->B = NULL; /* no Butcher table */

sundials/src/arkode/arkode_mristep_io.c

Lines 255 to 256 in c28eaa3

	step_mem->MRIC = NULL; /* no slow->fast coupling */
	step_mem->NLS = NULL; /* no nonlinear solver object */

(SPRKStep appears ok)

Also ERKStep is the only implementation that resets the adaptivity controller.

Expected Behavior:

Objects should be freed and the workspace size should be updated appropriately.
Also, ARKStep and ERKStep should be consistent about handling of adaptivity controller when ARKodeSetDefaults called.

Steps To Reproduce:

Call ARKodeSetDefaults after setting a Butcher table or nonlinear solver.

I've confirmed a memory leak with valgrind when ARKodeSetDefaults is called after ARKStepSetTableNum. Haven't tested further.