Package-level declarations

Base class every DSL builder extends — TileSchemaBuilder<T> and EventSchemaBuilder<T> both derive from this, one instance per DSL call (Column { }, SendNetworkRequest(...), etc.), responsible for producing the concrete schema T that call compiles down to.

Base class for every DSL "scope" receiver that accumulates a list of child builders and turns them into an immutable list of built schemas — TileSchemaBuilderScope/EventSchemaBuilderScope both derive from this. The DSL's trailing-lambda blocks (Column { SimpleText(...); Button(...) }, an event's events = { ... }) run against one of these: each nested DSL call constructs its own builder and registers it via addBuilder, and the enclosing call finishes by invoking build to collect every registered builder's output.