Optimize ZIO.attempt

[adamgfraser]

We can make this slightly faster by only looking up the definition of a fatal error if an exception is thrown.

[adamgfraser]

This does mean that if a fatal error does occur we need to execute one more workflow after that to get the definition of a fatal error so maybe this doesn't make sense.

[jdegoes]

I wonder if we should just intern it.

[adamgfraser]

Isn't the problem that the definition of a fatal error is itself a regional setting stored in a FiberRef so for correctness we have to look it up at some point? We could move the whole thing into the runtime but I don't think it is worth it. In microbenchmarks ZIO.succeed is about 10% faster than ZIO.attempt right now and with this change that difference goes down to about 5%.

[jdegoes]

All right, sounds good to me.