Make DI handler/decorator factories lifetime-aware (#329)

[iancooper]

Summary

Makes Darker's DI-backed handler and decorator factories lifetime-aware (Singleton / Scoped / Transient), matching Brighter, so handlers, decorators, and their injected dependencies (e.g. an EF Core DbContext) are created and released per their configured lifetime.

Fixes #329. Per ADR 0014-factory-component-lifetime (Accepted). Targeted at V5 — this is a breaking change to the public factory interfaces.

Defects fixed

1. Singleton components disposed after one query. The old factory Release disposed any IDisposable, so the next query received a disposed singleton → ObjectDisposedException. Darker's Release is now a no-op; container-managed singletons are never disposed by Darker (AC1/AC2).
2. Scoped deps resolved from the wrong scope. With the default Singleton QueryProcessor, the factory captured the root provider, so a Scoped DbContext never bound to the request. Each query now owns a child IServiceScope (via IServiceScopeFactory), so scoped deps resolve from the per-query scope even under a Singleton processor — verified with ValidateScopes = true (AC5).

Design

• The four DI factory roles merged into one internal ServiceProviderComponentFactory. A handler and its decorators share one per-query child scope, keyed on the per-query lifetime token via a ConditionalWeakTable (no per-query mutable state on the shared singleton factory).
• The scope is owned by a new IAmALifetime token and disposed exactly once in PipelineBuilder.Dispose(), invoked from QueryProcessor's using finally — so it is released even when the handler throws or the async pipeline is cancelled (AC7).
• No scope creep: default HandlerLifetime (Transient) and QueryProcessorLifetime (Singleton) are unchanged; no general IDarkerOptions service (BuildQueryProcessor passes options.HandlerLifetime straight into the factory).

Breaking change (public interfaces)

The factory abstractions gain an IAmALifetime parameter:

-IQueryHandler Create(Type handlerType);
-void Release(IQueryHandler handler);
+IQueryHandler Create(Type handlerType, IAmALifetime lifetime);
+void Release(IQueryHandler handler, IAmALifetime lifetime);

(same shape for IQueryHandlerFactoryAsync, IQueryHandlerDecoratorFactory, IQueryHandlerDecoratorFactoryAsync). New public IAmALifetime role + QueryLifetimeScope.

Testing

• dotnet build Darker.Filter.slnf -c Release → 0 errors.
• dotnet test Darker.Filter.slnf -c Release --no-build → 212 passing (Core 76 + Extensions 30, each on net8.0 and net9.0), 0 failed, 0 skipped.
• Coverage spans all three lifetimes × {handlers, decorators} × {sync, async} plus singleton-reuse and scoped-dependency scenarios (NFR4). AC1–AC10 all PASS — see specs/008-factory_component_lifetime/acceptance-verification.md.

Process

Built spec-first (Requirements → ADR 0014 → tasks → TDD implementation). Structural changes (Tidy First) landed separately from behavioural ones; each commit is purely structural, behavioural, or docs.

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