Better algorithm for extending PsiContour

[johnomotani]

In the temporaryExtend() method used to extend a PsiContour

hypnotoad/hypnotoad/core/equilibrium.py

Line 1802 in 4cef82a

def temporaryExtend(

at the moment the initial guess for new points is made by extrapolating from the positions of nearby points. It would be more accurate and probably more robust to use an ODE integrator to follow the flux surface, similar to how the separatrix is traced here

hypnotoad/hypnotoad/cases/tokamak.py

Lines 615 to 623 in 4cef82a

	# Integrate a distance "step" along the leg
	solve_result = solve_ivp(
	dpos_dl,
	(0.0, step),
	pos,
	rtol=0.0,
	atol=self.user_options.leg_trace_atol,
	)
	newpos = (solve_result.y[0][1], solve_result.y[1][1])