Do not even think of using the same cable for both the stepper power and the sensor signals!

Use a separate, shielded cable routed as far away from the stepper power cables as possible.

I think LDRs are pretty slow sensors - that should make it easier to filter out noise.

The lower the impedance of your sensor circuit, the less susceptible it will be.

Making it "balanced" will help - so the noise becomes "common-mode" and can easily be rejected.