But anyway, we've been comparing the speed of light over different directions since the 19th century. Modern relativity was created because of those measurements, and nowadays you can buy accelerometers and gyroscopes that work based on that constant speed.
I don't know anything about this, I just found a Wikipedia page [1]
Yeah, the one thing we tested again and again is that if there is any difference on the speed of light going and coming back, it must average to the same thing in every direction (actually in every circuit, with any number or directional changes).
There are some experiments that measure one-way speed even on the link you posted. The first measurement of the speed of light was one-way. Those are just low precision ones.
We can’t measure the speed from A to B directly (without sending something from B back to A wrt speed of light).
Can't measure one-way speed of light because you need to get the result back somehow (and that's also limited by speed of light). Usually we just send light and wait for it to bounce back.