Add tracing for expensive operations

[hackaugusto]

Some operations are inherently slow, like key generation. It is useful to know how much time these take. It would be useful to add tracing annotations to some of these operations.

The current motivation for the above is the miden-base tests, there we do key generation, and it is unclear how much time the test execution is part of the keygen, and the test itself. Having a bit more of insight on that would help decide when to mock / hard code a test key. (Ofcourse, this very example doesn't need tracing in crypto and can be done by hand, this is the motivating example, I think this would be useful in general).