shBitDepths property
Per-band spherical-harmonic bit depths, band 1 first.
Named choices live in fourdgsShLadders; for example,
fourdgsShLadders['balanced']! is the balanced list to pass here.
Empty applies no per-band depth: coefficients remain their exact eight-bit
values, the appended field is not emitted, and a profile's step_sh
remains compatibility metadata rather than an implicit coefficient grid.
Implementation
final List<int> shBitDepths;