feat(signal-slice): add lazySources

[joshuamorony]

EDIT: The note below has been resolved

NOTE: This is a draft PR due to one remaining issue and I'm not sure if it can be solved with this set up. I think the crux of the issue is that I am relying on a proxy to detect when the state object is accessed in order to trigger the lazySources to connect:

  return new Proxy(slice, {
    get(target, property, receiver) {
      if (!lazySourcesLoaded) {
        lazySourcesLoaded = true;
        connectSources(state, lazySources, injector);
      }

      return Reflect.get(target, property, receiver);
    },
  });

Although it still seems to work (the observable values are still set into the signal), it triggers the SIGNAL_WRITE_FROM_ILLEGAL_CONTEXT error:

ERROR Error: NG0600: Writing to signals is not allowed in a `computed` or an `effect` by default. Use `allowSignalWrites` in the `CreateEffectOptions` to enable this inside effects.

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This adds support for lazySources as discussed here: #196

It allows specifying sources and lazySources in the config - both are identical but the lazySources will not be supplied to the connect function until the state object has been accessed.

I have left this undocumented for now, ideally would like to have it used a little first. I think I also need to do a full sweep through and improve the docs as a whole as well.

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[nartc]

I can help with the issue

[nartc]

Check this commit for fix to issue

[joshuamorony]

Perfect, this seems to work, thank you! This should be ready to go now