Addition of an optional ISOTP layer (Optional request)

[rnd-ash]

As part of my custom Mercedes 722.6 Transmission control unit using a SAME54 processor, I created a rather generic ISOTP layer for (In theory) any device that uses an MCAN block, and uses RTIC:

https://github.com/rnd-ash/ultimate-nag52-fw-rs/blob/main/diag_common/src/isotp_endpoints/can_isotp.rs

So, as an idea, if I added the remaining parts of the ISO15765-2 specification to this layer, and maybe made the dependency of RTIC-Sync optional, would this be something that could be integrated into MCAN (or a child crate of MCAN?)

Currently, the way this layer works is it creates 2 structures. One is meant to be used by the CAN ISR (RxFifo message in), and the other part can be used in a async context, to read and write ISOTP messages.

Note that at the moment, the repository at the moment is quite a mess as I'm still trying to create the foundations for everything.

[epontan]

Neat! It is a nice idea, but ideally the MCAN specific parts could be abstracted away. It really just need to receive and send frames, right? I guess the embedded-can::nb::Can trait could be used for this if we would implement it in mcan. I'm not sure why it hasn't been implemented yet. It is a bit opinionated how transmit should be implemented.