Refactor core config, routing and balancer logic

Rework CoreConfigContextBuilder and CoreConfigManager to centralize and simplify outbound resolution and runtime config assembly. Key changes: handle CUSTOM profiles early, introduce ResolvedOutbound and resolvedOutbounds list, resolve routing-target outbounds separately, and unify normal/group/chain build flows into buildUnifiedConfig. Routing, DNS, inbounds, outbounds and balancer logic were modularized (configureInbounds/configureRouting/configureDns/configureFakeDns/configureLocalDns/etc.), balancer strategies and observability are consolidated, and domain pre-resolution/hosts handling preserved. Also added new balancer tag naming (TAG_BALANCER_PRE) and small API/utility adjustments across CoreOutboundBuilder, DTOs and enums to support the new flow. These changes improve clarity of the build pipeline, make custom/routing outbounds handling explicit, and prepare for richer policy-group balancing behavior.