Added wrappers for slices to allow for use of non-static memory for DMA

[Gip-Gip]

Recently needed to use DMA to ensure safe transmission of data in the off event that an interrupt triggers mid-data transfer(can cause substantial packet loss in my use case). This type ensures that the DMA transfer is complete before it is dropped by producing a pointer that needs to be fed back into the wrapper.

I haven't documented but if the feedback is good I can work on that later.

[Gip-Gip]

Also, do y'all think this would be better PR'd to the embedded-dma crate?

[Gip-Gip]

Also, do y'all think this would be better PR'd to the embedded-dma crate?

My only concern with this is I don't think DMA implementations are required to return the ReadBuffer/WriteBuffer only after DMAs are complete like the rp-hal implementation

[thejpster]

I don't see anything here that is RP2x specific, so this might not be the best place for it.

The documentation should probably also discuss the ramifications of calling std::mem::forget() on the wrapper.

[Gip-Gip]

I don't see anything here that is RP2x specific, so this might not be the best place for it.

The documentation should probably also discuss the ramifications of calling std::mem::forget() on the wrapper.

I'll take it to embedded_dma then