[sdk/logs] Replace mocks with real instances where possible

[pmcollins]

This change replaces some mocks with real instances in log testing. Motivated by looking at tests in this PR which uses mocks when they aren't strictly necessary. Would like to suggest that that change's tests use real types, but still be consistent with the other tests.

[ocelotl]

Actually, I think we want to use mocks as much as possible. When we test a particular code, ideally, we want to mock everything else. Mocks are cheap and this way we don't waste resources instantiating any real objects that could be mocked instead.

[pmcollins]

Actually, I think we want to use mocks as much as possible. When we test a particular code, ideally, we want to mock everything else. Mocks are cheap and this way we don't waste resources instantiating any real objects that could be mocked instead.

Happy to defer to the preferences of the folks in this SIG, and this is perhaps a larger topic than we might want to address here, but I think using real types in tests has lots of benefits over using mocks, mostly because real types more accurately reflect how the system will behave. This helps with verifying correctness at dev time, but it also helps with catching regressions later, and with test code demonstrating how to use an API. It's true that mocks can be faster than real types, especially types that perform I/O, but making I/O swappable for testing and using fakes during testing solves this problem (IMO it also nudges you to do other beneficial things like using dependency inversion and grouping related I/O code).