io: Update defmt to 1.0, rename feature from "defmt_03" to "defmt"

[chrysn]

We could do the defmt-1.0 update a bit more compatibly by just going to 0.3.100 (and possibly keeping the defmt_03 feature as a deprecated feature name), but given the discussion in #566 (comment), it may make sense to spool this for a single breaking >>0.6 bump, and use that to get rid of anything that'd be viewed as legacy in a 1.0 version.

One alternative to the hard cut would be to to keep a defmt_03 feature that merely pulls in 0.3.100, as a deprecated feature. If >>0.6 becomes a 0.7 that does the semver trick to 1.0, that feature could be removed as part of the 1.0 transition.

An extra deprecated defmt-03 feature is left in place mainly for embedded-io-async, which optionally pulls it in through the path-or-version dependency.

[rursprung]

thanks for taking care of this!

[rursprung]

i'd just mention the major version and skip minor&patch - there are no specific requirements here (that'd only make sense if you'd e.g. depend on 1.2.3 and really need something which was introduced only with that version; but 1 = 1.0 = 1.0.0).

(but that's just my opinion; i'm no maintainer)

otherwise this LGTM - thanks!

[chrysn]

Thanks for reviewing; your comments all being applied, I've taken the liberty to squash and rebase them into a sensible history for the maintainer team's review.

[rursprung]

perfect, thanks!

in the nit-picking territory: just note that with the two commits i'd usually expect that i could only build the first without the second but that wouldn't be the case here as then e-io-async would depend on a non-existent feature in e-io. so you might want to squash the two together completely or already use the defmt feature flag in the e-io dependency in e-io-async in the first commit.