panic in tests about color-eyre

[yaahc]

For right now there's not any particularly better way to handle this in tests built into color-eyre. We have this same problem in our crate at work and I fixed it by adding a std::sync::Once to govern the call to color_eyre::install().

https://github.com/ZcashFoundation/zebra/blob/main/zebra-test/src/lib.rs#L25

As for the panic in from that expect. I already have another plan for how I want to fix that. Basically, I'm going to change color-spantrace so that its theme can be passed in while printing the specific spantrace, rather than requiring it be set via a global. Then the color-eyre handler will have a theme stored locally so when it goes to print it it can just convert its theme and pass it in.

[akshayknarayan]

closing after reading conversation in #114.