Macro storable_nested_arrays 

storable_nested_arrays!() { /* proc-macro */ }

Generate Storable implementations for nested arrays of small primitive types.

Generates implementations for nested arrays like [[u8; 4]; 8] where:

• Inner arrays are small (2, 4, 8, 16 for u8; 2, 4, 8 for u16)
• Total slot count ≤ 32