A/B: azgauss vs fitgauss metacal reconvolution kernel #830

#829 exposes the metacal reconvolution kernel as a config knob (METACAL_PSF), defaulting to the fiducial fitgauss. azgauss (new in ngmix v2.4.1, pinned in #819) is pitched as a noise-robust drop-in replacement — worth an A/B before flipping the default.

Question: does azgauss change recovered m/c bias relative to fitgauss, and is it worth adopting as fiducial?

Mechanism: METACAL_PSF = azgauss vs fitgauss, digital-twin / image-sim comparison (calibrated m/c truth) per #813's methodology, complementary to real-data area once available.

— Claude, on behalf of Cail