Fix IResolver/IContainer injected into singletons capturing scoped container instead of root

[Copilot]

When a singleton is first resolved through a scoped container with WithoutThrowIfDependencyHasShorterReuseLifespan(), any directly injected IResolver/IResolverContext/IContainer dependency captures the scoped container instead of root — causing failures after scope disposal.

var container = new Container(Rules.Default.WithoutThrowIfDependencyHasShorterReuseLifespan());
container.Register<Service>(Reuse.Singleton);

using var scope = container.OpenScope();
var fromScope = scope.Resolve<Service>();

Assert.Same(container, fromScope.Resolver); // was FAILING — got scoped container instead of root

Root cause

ResolverContext.GetRootOrSelfExpr() gates the use of RootOrSelfExpr on ThrowIfDependencyHasShorterReuseLifespan (introduced for #378). When that rule is disabled, it falls back to ResolverContextParamExpr — the current scope's resolver — even for container interfaces directly injected into singletons.

Changes

• ResolverContext.GetRootOrSelfExprForContainerInterface() — new internal method identical to GetRootOrSelfExpr() but without the ThrowIfDependencyHasShorterReuseLifespan guard. Singletons must always receive the root container for direct interface injection regardless of captive-dependency rules.
• AddContainerInterfaces() — switched all five container interface wrappers (IResolver, IResolverContext, IContainer, IRegistrator, IServiceProvider) to use the new method.

The ThrowIfDependencyHasShorterReuseLifespan condition is preserved in the original GetRootOrSelfExpr() used by CreateResolutionExpression, so Lazy<ScopedService> inside a singleton still correctly resolves through the scope resolver (#378 behavior unaffected).

Tests added

GHIssue686_Singleton_service_resolved_by_scoped_container_not_root_container covering:

• IResolver in singleton resolved first via scope with WithoutThrowIfDependencyHasShorterReuseLifespan
• Same with default rules
• Resolved from root first, then scope (same singleton, correct resolver)
• IContainer variant
• Lazy<ScopedService> in singleton still works (regression for Inconsistent resolution failure #378)