Converters: SACC→2pt-FITS (byte-compared) + SACC↔OneCovariance glue#249

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cailmdaley wants to merge 3 commits into

feat/sacc-2-sacc-iofrom

feat/sacc-3-2pt-converter

Commits on Jul 10, 2026

feat(twopoint): SACC → 2pt-FITS converter, byte-compatible with cosmosis_fitting

cailmdaley
and
claude
committed
feat(one_covariance): SACC <-> OneCovariance file-format glue

cailmdaley
and
claude
committed
fix(twopoint): fail fast on tomographic/ξ-less SACC; pin covariance gather

cailmdaley
and
claude
committed