TokaMaker: Fix SciPy 1.18 compatibility in eqdsk.py geometry tracing

[Copilot]

Primary changes

SciPy 1.18 changed RectBivariateSpline.ev() to return a 1-d array (1,) instead of a 0-d array when called with scalar arguments. This breaks float() conversion in _trace_surfaces() at the magnetic axis point:

# Before (fails on SciPy >= 1.18)
Jt0 = float(Jt_interp.ev(Z0, R0))

# After (works on all versions)
Jt0 = float(Jt_interp.ev(Z0, R0).item())

This was the sole cause of the test_eqdsk_gfile failure on CI after the Ubuntu runner image update.

Secondary changes

None.

API changes

None.