feat: adapt probe code to allow for co64 box instead of stco

[theSuess]

@sunfish-shogi

This allows for the correct probing of videos recorded on modern android devices

I'm not sure if this covers all edgecases (especially with videos >4Gi) but this was sufficient for my usecase.

Let me know if you think there is a better approach!

[sunfish-shogi]

Thank you for your pull request!!

I will update probe_test.go after merge.