[WIP] Add support for runtime filtering

[t-moe]

I want to discuss how a possible API could look, to set a global min log level, used for runtime filtering.

This PR adds set_global_log_level which stores the minimal log level in a static AtomicU8.

Other approaches I could think of:

• Pass the LogLevel of the message to the Logger impl and let them figure out where they want to store the min log level. like in Log::enabled of the log crate

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Sidenotes:

• In the current implementation I use the IdRanges struct that I have added in an earlier PR, but I realize now, that I could also pass the LogLevel from the macro implementation directly.
• The current implementation works on the target, but for the tests to work in CI it would obviosly need some more work.