You can desensitize the hall sensor for a fixed period after initiating the spark,
add a global boolean to mask out the hall signal. Make the interrupt
routine use this to filter out any pulses for the relevant window - the
main loop code sets and resets this flag at the right points.
The main problem will have is interference, which means shielded cables for
sensors are good, keeping HT stuff well away from low voltage stuff. RF filtering
on the inputs (something like a 100pF capacitor between signal and ground at
the board) will reduce problems too.