feat: SimulatorImaging.via_tracer_from auto-defaults xp from parent use_jax

Changes via_tracer_from(xp=np) to via_tracer_from(xp=None) with auto-fallback
to self._xp inherited from aa.SimulatorImaging. When the simulator is
constructed with use_jax=True, via_tracer_from now routes xp=jnp through
tracer.padded_image_2d_from and via_image_from without the user passing it
explicitly.

Depends on Jammy2211/PyAutoArray PR adding the use_jax constructor flag +
_xp property to the parent aa.SimulatorImaging.

Part of Phase 2 PR 2 of z_features/jax_user_intro.md.

Issue: PyAutoArray#334

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 2 people

autolens/imaging/simulator.py

@@ -22,7 +22,7 @@
 
 class SimulatorImaging(aa.SimulatorImaging):
 
-    def via_tracer_from(self, tracer : Tracer, grid : aa.type.Grid2DLike, xp=np) -> aa.Imaging:
+    def via_tracer_from(self, tracer : Tracer, grid : aa.type.Grid2DLike, xp=None) -> aa.Imaging:
         """
         Simulate an `Imaging` dataset from an input `Tracer` object and a 2D grid of (y,x) coordinates.
 
@@ -50,6 +50,9 @@ def via_tracer_from(self, tracer : Tracer, grid : aa.type.Grid2DLike, xp=np) ->
             in order to generate the image of the galaxies via their light profiles.
         """
 
+        if xp is None:
+            xp = self._xp
+
         tracer.set_snr_of_snr_light_profiles(
             grid=grid,
             exposure_time=self.exposure_time,