Too much complexity and too many type arguments

[samcrow]

A lot of the Cyphal implementation code in this repository has interfaces that look confusing and are difficult to use correctly.

In particular:

• Clock, Instant, and Duration types wind their way through the entire stack from the application to the driver.
• There are many options for transfer ID trackers, numbers of various things that can be stored, and other settings that lead to very long types like this:

  pub type UavcanNode = BasicNode<
  CoreNode<
      Stm32MicrosecondClock,
      CanTransmitter,
      CanReceiver,
      TransferIdFixedMap<CanTransport, TRANSFER_IDS>,
      QueueDriver,
      MAX_PUBLISHERS,
      MAX_REQUESTERS,
  >,
  >;

• There are too many error types, and they are too complex. They handle driver errors, subscription-related errors, and out of memory errors from many different layers.

These are some possible changes that would help with this:

• Make Instant and Duration non-generic. They could just be 32-bit numbers of microseconds. That would overflow about every 35 minutes, which probably won't be a problem.
  • Is there any good way to make the Clock type parameter not so widespread?
  • Use a function pointer instead: fn() -> Instant (for embedded applications, this would not be compatible with drivers that use objects to restrict access to resources)
• Move the Clock and other type-based settings and constants into some kind of Config type, so the Nodes don't need so many different type parameters
• Remove MinimalNode and rename other node types (the node types have confusing names, and I don't know when anyone would actually use MinimalNode instead of one of the other two)
• Make the error types a little less informative so they can be simpler, possibly by having a single non-generic value for driver errors