fix: traced instance attributes never land in pytree aux data

[Jammy2211]

Part of PyAutoLabs/PyAutoLens#678 phase B — one of the two defects that killed the cluster image_plane_solved gradient cell on the A100s (the other is the PointSolver padded-row fix, PyAutoLabs/PyAutoLens#685).

Problem

_build_instance_pytree_funcs classifies attributes never declared on a walked model as constants → pytree aux data. Attributes derived inside __init__ from prior parameters (e.g. NFWMCRLudlowSph computing kappa_s/scale_radius from a free mass_at_200) are exactly such attributes, and under a trace their values are tracers. Aux crosses transformation boundaries as raw Python references, so a custom_jvp rule's inner jax.jvp receives the instance with a stale LinearizeTracer in scale_radius and raises UnexpectedTracerError the moment it is consumed (1.0 / self.scale_radius).

Only gradient paths hit it (Nautilus never runs a JVP rule), and only models with derived-in-__init__ attributes (galaxy-scale Isothermal cells were unaffected) — which is why this survived until the first cluster MCR-halo gradient search.

Fix

At flatten time, any attribute whose value is a JAX array or tracer is promoted to a dynamic child, whatever the classifier says — a traced value is never safe aux. Concrete Python values keep the constant behaviour, so control flow on constants (sorted(..., key=lambda g: g.redshift), isinstance dispatch) is untouched.

Verification

• Full test_autofit/: 1641 passed, 2 skipped.
• New assertion script autofit_workspace_test/scripts/jax_assertions/derived_attribute_leaves.py (JAX tests live there per test: delete jax-using unit tests (moved to autofit_workspace_test) #1247): fails with UnexpectedTracerError before this fix, passes after.
• The Sensitivty: Results and Database #678 cluster cell's value_and_grad completes after this fix (paired with fix: sanitize padded rows in the PointSolver implicit-diff rule for reverse mode PyAutoLens#685 for finite gradients).

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https://claude.ai/code/session_01DnTmLoJjJgMTze5uAbg1Jd