[BUG] Inconsistent log formatting for `WARNING` and `CRITICAL` categories

[asnare]

The Python logging system has WARN and FATAL levels, as convenient aliases for WARNING and FATAL. At the moment the custom logging configuration that Blueprint installs is inconsistent in how these categories are logged:

• If color output is disabled, the names WARNING and CRITICAL are used, as is the norm for Python application.
• If color output is enabled, the names WARN and FATAL are used instead. This is inconsistent with both the uncolorized output and Python norms.

Although the terms WARN and FATAL are slightly shorter, the benefit is probably outweighed by diverging from the expected norms of the ecosystem and inconsistent terms depending on the configuration.