add support for defmt log using a new feature

[Georges760]

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[eval-exec]

Hello @Georges760 Will this PR cause performance loss?

[eval-exec]

I exeucted cargo bench on master, then execute cargo bench again on your PR, it seems that some bench case report performance loss about 20%, and some case performance improved

[Georges760]

Nope it is just a formatting for debug purpose, so in production should not be enable.

[Georges760]

It is like the Serde derive, just an additional feature optional

[eval-exec]

Nope it is just a formatting for debug purpose, so in production should not be enable.

OK, it's seem that cargo bench's result is not stable.