feat: replace reflection-based trigger discovery with source-generated registry

[Copilot]

The unused-trigger analysis in StateMachineAnalysis used Assembly.GetTypes() and Type.GetProperty() at runtime to discover concrete trigger subtypes — blocking full AOT/trim compatibility and requiring [RequiresUnreferencedCode] / [UnconditionalSuppressMessage] suppression annotations.

New: FunctionalStateMachine.Core.Generator

A Roslyn incremental source generator that discovers trigger type hierarchies at compile time and replaces all runtime reflection.

• Detects StateMachine<TState, TTrigger, ...>.Create() calls (both 3-param NoData and 4-param with-data variants)
• For each unique TTrigger, finds all non-abstract concrete derived types via Roslyn symbol APIs
• Skips types inaccessible from the generated initializer (private nested types filtered out)
• Skips generation if [ModuleInitializerAttribute] is unavailable (graceful no-op on netstandard2.0 without polyfills)
• Packaged inside FunctionalStateMachine.Core at analyzers/dotnet/cs — applies automatically to all NuGet consumers

Generated output:

// <auto-generated />
namespace FunctionalStateMachine.Core.Generated
{
    internal static class TriggerTypeRegistrationBootstrap
    {
        [ModuleInitializer]
        internal static void Initialize()
        {
            TriggerTypeRegistry.Register<global::MyApp.MyTrigger>(new[]
            {
                typeof(global::MyApp.MyTrigger.TriggerA),
                typeof(global::MyApp.MyTrigger.TriggerB)
            });
        }
    }
}

Core library changes

• TriggerTypeRegistry (new): static TTrigger → Type[] registry populated by the generated initializer
• StateMachineAnalysis: using System.Reflection removed entirely; AnalyzeUnusedTriggers reads from the registry and silently skips if not populated; [RequiresUnreferencedCode] / [UnconditionalSuppressMessage] annotations removed
• Bug fix: GetTriggerTypeName was calling .GetType().Name on Type objects (returning "RuntimeType" in error messages); now returns the actual type name

AOT impact

IsAotCompatible=true (net8.0+) is now fully clean — zero remaining IL2026/IL2070 suppressions needed.

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