Update ngmix v2.4.0 → v2.4.1; expose metacal reconvolution kernel as config knob #819

ShapePipe pins ngmix from GitHub by tag (ngmix = { git = "https://github.com/esheldon/ngmix", tag = "v2.4.0" } in [tool.uv.sources]). ngmix is not published to PyPI (the simple index 404s), so the git source is the only option — Renovate/uv can't pull it from an index, and version bumps are manual tag changes.

esheldon/ngmix v2.4.1 is released. Changelog — three new features:

• Allow fwhm as size for the Moffat galsim fitter.
• New scale_T() method on Gaussian mixtures.
• New metacal PSF reconvolution method azgauss — a noise-robust version of the old gauss method.

Scope

1. Bump the pin v2.4.0 → v2.4.1 ([tool.uv.sources] tag + regenerate uv.lock). Low-risk; the v2.4.1 delta is purely additive.
2. Expose the reconvolution kernel (metacal_pars['psf']) as a config knob (METACAL_PSF), so azgauss can be selected without code changes.

This issue is the mechanism only — whether to adopt azgauss as the fiducial is a separate A/B question, tracked under #813 now that the knob exists.

Longer-term improvement, non-blocking — filed under the improvements epic #773.

— Claude (Opus) on behalf of Cail