Specialized Baes anisotropy kernels

See Units, shapes and model contracts for units, shapes, domains and backend boundaries, and Quickstart for executable minimal examples.

BaesEta2AnisotropyModel([submodels])	Baes--van Hese anisotropy with eta fixed to 2.
DEFAULT_BAES_ETA2_KERNEL_N_QUAD	Default fixed quadrature node count for the eta=2 Baes kernel.
baes_eta2_kernel_appell_reference(u, R_pc, ...)	High-precision reference evaluation using mpmath.appellf1.
baes_eta2_kernel_jax(u, R_pc, beta_0, ...[, ...])	Evaluate the eta=2 BAES kernel from its Appell-F1 representation.