Function q_index_of 

pub fn q_index_of(name: &str) -> Option<usize>

Map a qN identifier (1 ≤ N ≤ 64) to its 0-based slot index in the q-vars array. Returns None for any non-qN name or out-of-range N. Used by the bytecode VM compiler and by MilkContext’s Context impl to bypass HashMap probes for the q-channel reads/writes that dominate per_frame state passing.