Add visibility-space iterative LM engine (interferometer phase 2a)

Adds al.pc.IterFitDpsiSrcInterferometer: the joint source+dpsi
Levenberg-Marquardt loop for interferometer data, run entirely in the
real-space normal-equation space (F = A^T Wtilde A via the sparse
operator, D = A^T dirty_image, precomputed d^H C^-1 d) so no
per-candidate NUFFT is needed and cost scales with real-space pixels.
Re-traces through the corrected lens (InputPotential) each accepted
step; optional gauge constraints via the shared KKT step; Laplace
evidence with complex-noise normalization. Chi2 identity certified
against the direct visibility chi2 in tests. Adds
IterDpsiSrcInvInterferometerAnalysis + docs entries.

Phase 2a of #623 (parent epic #618). Cao et al.
2025 citations maintained.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: 2 people

autolens/potential_correction/__init__.py

@@ -31,3 +31,9 @@
 from autolens.potential_correction import dense_util
 from autolens.potential_correction.iterative import IterFitDpsiSrcImaging
 from autolens.potential_correction.iterative import IterDpsiSrcInvAnalysis
+from autolens.potential_correction.iterative_interferometer import (
+    IterFitDpsiSrcInterferometer,
+)
+from autolens.potential_correction.iterative_interferometer import (
+    IterDpsiSrcInvInterferometerAnalysis,
+)