I want to merge API-crates into one.

[boozook]

As we already know, modularity is PITA (#224).
Subject, I want to merge API-crates excluding sys (and some other, see below) into the playdate crate. Currently playdate is an umbrella crate that reexports all other API-crates. Also there is "common traits" and other things used in all of them currently living in sys as common dependency. And some of those common things are just copy-pasted and live in several crates, but not in sys. This is not very good.

List of API-crates which could be excluded from merge:

• sys
• callbacks
• allocator
• ui-components?

As bonus I'll get easy swap sys<-->mock dependency of the playdate and others just via patch on workspace level.

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