fix: check StateDiagram inheritance semantically, not syntactically

[spirifoxy]

[StateDiagram] is silently ignored when the attributed record's base type is not literally named LogicBlockState and that base is not declared in the same file. The generator falls through to the unrelated IsLogicBlockCandidate path and writes a stub diagram containing only the initial state.

Reproduction

// SharedBase.cs
public abstract record SharedBase : LogicBlockState;

// MyLogic.cs
public partial class MyLogic : LogicBlock {
  [StateDiagram]
  public abstract partial record MyState : SharedBase; 
  ...
}

Gives

@startuml MyLogic
state MyLogic {
  state Dark
}

[*] --> Dark
@enduml

Changing : SharedBase to : LogicBlockState produces the correct diagram with every state and transition.

Fix

Move the inheritance check from the syntax predicate into the semantic transform .

• IsStateDiagramCandidate now only checks for the attribute.
• DiscoverStateGraph verifies inheritance via CodeService.GetAllBaseTypes, the same helper it already uses a few lines further down, and returns null if the type is not a logic block state.

[Bastani]

Thank you for your submission, I made a few comments about the changes, looks good otherwise!

[Bastani]

I think this fix shows a bigger problem with CodeService.InheritsFromByName, it only checks within the same file. There's a similar bug with if you were to make a base LogicBlock.

I think the CodeService.InheritsFromByName should probably be removed to discourage people from using it.

If you're open to fixing that in this PR, that would be great, otherwise I can open another after this is merged.

[spirifoxy]

Done, fixing that also turned up two more partial-class bugs

• a Start call in a second file silently dropped the diagram
• every partial calling Start would have emitted its own diagram

Both are fixed

[spirifoxy]

Thank you for your submission, I made a few comments about the changes, looks good otherwise!

Thanks for the review! All three are addressed