test: Lenstool dPIE parity script (6 numerical legs)

[Jammy2211]

Summary

Adds scripts/cluster/lenstool_parity.py — the numerical parity check backing the Lenstool-native dPIE parameterization shipped in PyAutoLabs/PyAutoGalaxy#487 (issue PyAutoLabs/PyAutoGalaxy#485). Six legs, all asserting at 1e-3 or tighter and currently passing at 1e-7–1e-10:

1. from_lenstool conversion parity (b0 prefactor, sqrt(3/2) sigma relation via the independent cosmology.velocity_dispersion_from, emass→epot vs Lenstool's set_lens.c formula).
2. Spherical deflection vs quadrature of the independently-ported convergence.
3. Analytic enclosed-convergence closed form (ra→0).
4. Elliptical deflections vs finite-difference gradient of the analytic pi05 potential.
5. analytical_hessian_2d_from vs deflection finite differences (profile frame; frame convention documented in the script).
6. The port's original Lenstool-generated reference deflections re-derived through the full conversion layer.

Includes a documented recipe (.par stanza) for regenerating true Lenstool reference values with a Lenstool build.

Scripts Changed

• Added: scripts/cluster/lenstool_parity.py — pure numpy, no dataset dependencies, runs in ~20 s.

Merge gate

Library-first: merge PyAutoLabs/PyAutoGalaxy#487 before this PR (the script imports from_lenstool / the analytic potential).

Validation checklist (--auto run — in-session directives, no separate plan pre-approval)

• Effective level: supervised (header: supervised, cap: feature → supervised)
• Gate: script passes end-to-end against the library branch (6/6 legs) · Heart YELLOW acked in-session
• Human: merge after the library PR

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