feat: allow pretty print logging in tests

[hstove]

This allows STACKS_LOG_PP=1 to be used in tests.

We previously had two make_logger functions - one for tests and one for not tests. The only differences were:

• The tests logger didn't allow pretty printing
• The tests logger uses slog_term::TestStdoutWriter

This PR makes it so that we only have one make_logger function. Inside of that function, I've added a flag to use TestStdoutWriter in tests.

[obycode]

I think the canonical way to do this is a little cleaner:

let decorator = {
    #[cfg(not(any(test, feature = "testing")))]
    {
        slog_term::PlainSyncDecorator::new(std::io::stderr())
    }
    #[cfg(any(test, feature = "testing"))]
    {
        slog_term::PlainSyncDecorator::new(slog_term::TestStdoutWriter)
    }
};

[jcnelson]

Even better would be to put the entire declaration block into its own function, and have one function for testing and one for prod.

[hstove]

Good call, I pulled it out into its own function 👍🏼