Move split/single output generation and writing logic to
packager/produceOutput.ts to keep packager.ts focused
on the high-level orchestration flow.
- Create produceOutput module handling both output modes
- Simplify packager.ts from 227 to 181 lines
- Update related tests to use new dependency structure
Adds a size-based output splitter via --split-output (kb/mb) and writes numbered parts without splitting within a top-level folder.
Also updates metrics aggregation for multi-part output and adds unit tests.
