✨ Add boxed module

[zeenix]

This is an abstraction over heapless::pool::boxed and alloc::boxed.

[zeenix]

Keeping this in draft until heapless 0.9 is released (hopefully with my needed fixes) and we can then switch to using that. I'll also tackle the MSRV issue (probably just need bumping again).

[zeenix]

@mkj If you adding the 👀 reaction to the PR means that you might be interested in this feature, I could use a second pair of eyes on this so if you could review it, that would be very helpful. 🙏

[mkj]

Thanks for the ping - not sure if I'll be using boxed, though other bits of mayheap look useful for me in a couple of crates.

This PR looks good. A couple of minor thoughts.

[zeenix]

This PR looks good. A couple of minor thoughts.

That was an extremely helpful review. Thanks so much! If you could just have one last look before I merge, that would be great.

[mkj]

Looks good. I think the const {} is still needed. It fails without it for me (the github action heapless test should have portable-atomic feature)

cargo --locked test --no-default-features --features heapless,serde,portable-atomic
..
error[E0277]: the trait bound `BoxBlock<u32>: std::marker::Copy` is not satisfied
 --> src/boxed.rs:16:1
  |
8 | box_pool!(MyBoxPool: u32, 2);
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::marker::Copy` is not implemented for `BoxBlock<u32>`

[zeenix]

Looks good. I think the const {} is still needed. It fails without it for me

Oh right, good catch! I had forgotten that portable-atomic is required for this module so was not really testing it at all. 🤦

(the github action heapless test should have portable-atomic feature)

Great idea. Done!

[zeenix]

@mkj Many thanks for your help! 🙏👍