refactor: use auto back-rotation in deflection methods

[Jammy2211]

Summary

Update all deflection methods to use the new @aa.grid_dec.transform(rotate_back=True) decorator from PyAutoArray, removing manual self.rotated_grid_from_reference_frame_from(...) calls. Net reduction of ~47 lines across 12 profile files.

Depends on: PyAutoLabs/PyAutoArray#272

Shear methods (which use angle=self.angle(xp) * 2) and the MGE abstract class (which rotates via self.mass_profile) are left unchanged — these use non-standard rotation that the decorator doesn't cover.

API Changes

None — internal changes only. All deflection methods produce identical numerical results.

Test Plan

• 834 PyAutoGalaxy tests pass
• 12 new regression tests with exact numerical values for Isothermal, NFW, PowerLaw
• All existing profile tests (494) continue to pass

Full API Changes (for automation & release notes)

Changed (internal only)

• 13 deflection methods across 12 files now use @aa.grid_dec.transform(rotate_back=True) instead of manually calling self.rotated_grid_from_reference_frame_from(...)
• Files changed: isothermal.py, power_law.py, power_law_core.py, power_law_broken.py, dual_pseudo_isothermal_mass.py, dual_pseudo_isothermal_potential.py, nfw.py, gaussian.py, chameleon.py, external_shear.py, cse.py, sersic.py

Added (tests)

• test_autogalaxy/profiles/mass/test_transform_rotate_back.py — 12 regression tests covering Isothermal, NFW, PowerLaw, ExternalShear, Gaussian with exact numerical values

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