Release embedded-io 0.7

[chrysn]

Contributes-To: #566

This is a Draft PR until

• I've satisfied all the interdependencies between other crates from the same workspace (as they have both version and path, they have to change their dependency version in the same PR),
• I've updated the date to my best guess of the release, and
• I think we won't wait more for any new changes (embedded-io: API stability and 1.0.0 release #566 has been open for a while, so that shouldn't be too long).