Core interfaces, resource abstractions, and capability models for iconn integration environments

Core runtime, YAML topology parser, lifecycle orchestration, and connector registry for iconn

Database connector providing embedded H2 databases, DataSource lifecycle, and schema migration execution

Email connector providing in-memory captured mailboxes and message verification

HTTP resource connector providing zero-dependency mock HTTP servers, request matching, and fault injection

JUnit 5 extension for declarative iconn integration testing, lifecycle hooks, and resource injection