Reference fixtures and generation code for AbstractCosmologicalEmulators.jl and jaxace

Frozen numerical test fixtures and their generation code for AbstractCosmologicalEmulators.jl and jaxace. Includes complete committed source snapshots, tests, generators, dependency declarations, original licenses, provenance and per-file SHA256 checksums. 252 text fixture/metadata files; 440 archive files in total. Julia commit 42fb48d4337d344808d2b657d7fa86852badf238; JAX commit f32961ffc93c7a6077873714312ec2bb5cbcc68c. No git history, local modifications, installed environments or trained emulators are included. This is not a package release. Historical fixtures are preserved unchanged. Some generation scripts require historical package/solver versions documented in their provenance; not every historical fixture can be regenerated from current APIs alone. See the archive README. CI download integration is a separate step. Archive SHA256: 10f59f1e0544c5f682953e66fa4ea40eba24a13297459cdb34510be592478294. Julia artifact git-tree-sha1: 57b2eb88f55763a47273e26b1b88c3c539539c8a.