Confidential-ml-utils

Strictly speaking, this contains a breaking namespace change: `stackTraceExtractor` ↦ `stack_trace_extractor`, but that API is unused.

- To address https://github.com/Azure/confidential-ml-utils/issues/56, implement a `category`-aware version of logging with a keyword-only argument for the `category` extension and signatures aligned with base classes in all supported python versions
- Add unit tests for non-`category` aware logging
- Fix `extra` so that it is not overriden by a `prefix` only dictionary