Typed semantic intermediate representation (IR) for plsql-intelligence.
The IR is one step removed from the raw AST emitted by plsql-parser:
the AST is syntactic, the IR is semantic. Downstream product surfaces
(lineage, SAST, docs, bindgen, CI/CD) consume the IR rather than
re-walking ASTs, so name resolution, overload selection, and Oracle
catalog cross-checking happen in one place.
introduces the top-level container types:
[SemanticModel], [FileModel], and [SchemaModel].
adds the [Declaration] enum and its variant payloads in the
[decl] module. Statement lowering arrives in.