Add support for verbose trace level logging

[rh101]

Describe your changes

The most verbose log level at the moment is LogLevel::Debug, and while this serves its purpose, it is not suitable for trace-level logging, as it would end up with too much log spam, along with the possibility of revealing information that otherwise should not be revealed in a release/production version of an application.

This PR adds LogLevel::Trace, which is specifically for the purpose of verbose logging.

@halx99 If you accept this PR, do you want a color associated with the trace messages? If so, which color should be used for this?

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[halx99]

about color, I think we can refer to spdlog.

[rh101]

about color, I think we can refer to spdlog.

They seem to use white foreground color for the trace level \x1b[37m, which seems to be common for trace messages. I'll set it to that unless there are any objections.

Spdlog also uses cyan \x1b[36m for debug level. Should that be used too?

[rh101]

Debug level output is set to cyan, and Trace level output is set to white, both of which seem to be used in other apps (spdlog and Android etc.)