Interface abstraction

[Craftplacer]

Resolves #18
Resolves #23

[Craftplacer]

Key changes of this pull request so far:

• SaneIsolate is split into implementation of Sane (SaneNative) and a class for managing the isolate itself (SaneIsolate)
  • SaneDevice with text info and methods were introduced, list of known device types is also available at SaneDeviceTypes
• Sane is now an abstract interface with properly documented members, the implementation became SaneSync
  • SaneSync is used by SaneIsolate similar to before, sharing code.
• Name lookup for SANE devices was replaced with just handing out the pointer address (which is only visible if you know the NativeSaneDevice type)
• SaneNative uses device names for referencing devices (since we don't want to expose anything we don't want the developer to use themselves)
• set_io_mode is not exposed anymore (we should handle it ourselves)
• The isolate properly exits now

[Jupi007]

Why did you replaced SaneHandle with a simple int? I prefer the class encapsulation of that concept.

[Jupi007]

Little nitpicks :)
Sorry for the delay, I was too busy...

[Jupi007]

Maybe create a _handleOrOpen method/getter?

[Craftplacer]

I disagree, because the behavior is already so apparent (_handle ??= _open() = "if handle is not null, return handle, otherwise open new handle"), it wouldn't bring much benefit other than it being an explicit method call.

[Craftplacer]

Unless you want to combine _open() and this behavior, then maybe we could do that, other than that, I don't see much reason. Happy to discuss.

[Jupi007]

Sorry I totally forgotten your PR... too busy 😓

What I mean is to remove this line duplicated in almost each function:

- final handle = _handle ??= _open();
- dylib.sane_function(handle);
+ dylib.sane_function(_handleOrOpen);

The goal is just to make the code less verbose.

And yes, this could be merged with open, or inside a dedicated getter/method 🤔