test: cover EffectJunction railway, runners, and effect builder overloads

[Theauxm]

Summary

Adds direct tests for code paths that were sitting in the 60-80% range:

• EffectJunction.RailwayJunction — non-ServiceTrain train throw, null-Metadata throw, happy-path metadata population, and the JunctionEffectRunner.Before/After callbacks
• JunctionEffectRunner.BeforeJunctionExecution / AfterJunctionExecution — dispatch to active providers
• LifecycleHookRunner.OnStateChanged — exception in one hook is logged and the next hook still runs
• TraxEffectBuilder.AddEffect(factoryInstance) and the three AddJunctionEffect overloads
• TraxEffectBuilder.AddLifecycleHook overloads, including the InvalidOperationException thrown when T implements neither ITrainLifecycleHook nor ITrainLifecycleHookFactory
• The AddScopedTraxJunction / AddTransientTraxJunction / AddSingletonTraxJunction runtime-Type overloads

Also adds NSubstitute to Trax.Effect.Tests.Integration (already in use elsewhere in the workspace).

Trax.Effect (main lib) line coverage moves from ~88% to ~94%. Aggregate Effect coverage moves from ~80% to ~84% — the remaining gap is RabbitMQ broadcaster (no infra) and DataContext logging providers (postgres-backed).

Test plan

• dotnet test — all suites pass (16 new)
• dotnet csharpier check . — clean

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[traxsharp]

This PR is included in version 1.34.0