Feature/bitfield change detector factory

[matt05d]

Generate change detection factory for schemas with leveled bitfields

Summary

• The C# source generator can now emit a static {SchemaName}ChangeDetection factory class that creates a BitfieldChangeDetector pre-configured with all bitfield points that have level annotations
  (Warning/Error/Emergency). This eliminates the need for consumers to manually wire up tracking for each point — the factory stays in sync with the schema automatically.
• Factory generation is opt-in via an MSBuild property, since it requires the consuming project to provide a BitfieldChangeDetector implementation. This keeps the Modspec schema language-agnostic —
  the JSON schema itself is unchanged, and generators for other languages (e.g. Python) can implement their own equivalent using the same level annotations. Modspec itself remains self-contained and does not
  depend on any specific change detection runtime.

Usage

Consuming C# projects opt in by adding the following to their .csproj:

  <PropertyGroup>
      <ModspecGenerateChangeDetectionFactory>true</ModspecGenerateChangeDetectionFactory>
  </PropertyGroup>

  <ItemGroup>
      <CompilerVisibleProperty Include="ModspecGenerateChangeDetectionFactory" />
  </ItemGroup>

The consuming project must provide a BitfieldChangeDetector class in the Modspec.Model namespace with a Track method matching the following signature:

  BitfieldChangeDetector<TClient> Track<T>(Func<TClient, T> getter, Func<T, Level> getLevel)
      where T : struct, Enum

Generated output example

For a schema named SomeBms with bitfield points StringErrors1 and StringErrors2 that have level annotations:

  public static class SomeBmsChangeDetection
  {
      public static BitfieldChangeDetector<SomeBmsClient> CreateDetector()
      {
          return new BitfieldChangeDetector<SomeBmsClient>()
              .Track(c => c.StringErrors1, v => v.GetLevel())
              .Track(c => c.StringErrors2, v => v.GetLevel());
      }
  }

Test plan

• Modspec builds with factory generation disabled (default) — no BitfieldChangeDetector reference in generated output
• Modspec builds with factory generation enabled — factory class generated for schemas with leveled bitfields
• Three new test cases verify factory creation, change detection, and highest-level reporting
• All 13 tests pass