Improve compiler lint and error classification (#208)

* Warn on non-null assertions

- Surface non-null assertions during linting without making them blocking.

- Preserve existing assertion sites for opportunistic cleanup.

* Classify internal compiler errors

- Export InternalCompilerError and migrate compiler invariant throws without changing messages.

- Rename the native cache test to match cc.ts and update test scheduling references.

- Document test placement by unit, package integration, and cross-package scope.

* Fix internal compiler error classification