Function write_binary_field 

pub fn write_binary_field(data: &[f64], dims: [u32; 3], ndim: u8) -> Vec<u8> 

Write a f64 field with a binary header.

Returns the complete byte stream: [header (24 bytes)] + [payload]. The header checksum is computed automatically.

• data – the field values in row-major order
• dims – [nx, ny, nz] (set unused dims to 1)
• ndim – number of active dimensions (1, 2, or 3)