Package refactoring

Refactor into `packages/`:

1.`@itk-wasm/dicom` (currently in `dist/`), then incorporate the ./io/internal/pipelines/image/read-dicom/CMakeLists.txt
2. `@itk-wasm/image-io`
3. `@itk-wasm/mesh-io`
4. ~`@itk-wasm/polydata-io`~ - no longer supported
6. `@itk-wasm/mesh-to-polydata` (migrate to [remote module repository](https://github.com/InsightSoftwareConsortium/ITKMeshToPolyData))
7. Migrate `src/core` -> `itk-wasm`

Then consolidate duplication when possible, e.g. *BuildZstd.cmake*.

Then configuration as a npm/pnpm workspace.