What do you actually need? 1 microsecond with “decent bit” is not exactly a lot of information. An oscilloscope would fit that perfectly. How do they not work how you want them to? Who told you that you need something else?
What you are talking about is nothing special at all and not following a charging curve. The curve automatically looks the way it does when charging CCCV. Constant Current -> Constant Voltage.
Don’t charge LFP to 4.2 volt! The crude “check voltage and if below 3.6 V keep charging” is okay too as long as the maximum current is within battery spec. But measure while charging, don’t turn that off to measure the open circuit voltage.
This is by far the best option for awkward connectors. You could even remove the pins and put the new cables in by opening the crimp and soldering the new ones without any splice.
I think that would be too much. A bowling ball is really smooth. It would not roll as well with such deviations all over the place.
At a diameter of 22 cm, the roughness would have to be in the order of 0.3 mm, which would not just be visible due to the distorted reflections, it would even be audible while rolling.