Function emit_time_multiplexed 

pub fn emit_time_multiplexed(name: &str, a: &Grid, b: &Grid) -> String

Emit the time-multiplexed array as combinational RTL: every tile computes BOTH fabrics’ drives and muxes each channel on ctx; the result muxes the two fabrics’ output taps. One silicon array, two programs — selected by a configuration bit.