Feature request: lock certain parameters and exclude them from calibration

[Bougakov]

Hello. I'd like you to consider a feature request: let the user "lock" certain parameters and make an algorithm exclude them from calculations. For example, I am 100% certain my "steps per mm" value is correct, so I'd prefer OpenDACT to avoid touching it. When a z-probe isn't very reliable and produces "noisy" measurements, OpenDACT ends up increasing "steps per mm" incrementally without much success (usually it makes things worse). If that could be "locked", it'd force the program to try other tweaks instead.