KillerPDF 1.9 "Overkill": the engine is ready for contributors

[SteveTheKiller]

KillerPDF 1.9 "Overkill" has reached the point where I want to open the door wider to contributors.

The biggest architectural work is now in place. KillerPDF.Engine owns PDF rendering, text and image placement extraction, document reading, editing, and writing. PDFium and PdfPig have been removed from the application path. The engine also includes its own OCR path and a vendored JPEG 2000 decoder.

The current numbers are encouraging:

• On the 649-file conformance collection, KillerPDF.Engine rendered 614 files, skipped 35, and failed on 0. PDFium rendered 600, skipped 41, and failed on 8.
• On the 600 first pages both renderers completed, engine render time was 12.196 seconds versus 12.280 seconds for PDFium. That is rendering parity within normal run-to-run noise.
• The identical-input whole-pass measurement is still about 3% behind PDFium, so there is useful performance work left.
• In a fresh text extraction benchmark across 374 PDFs completed by both engines, KillerPDF.Engine took a 3.80 second median versus 6.67 seconds for PdfPig. That is about 43% less time and 1.75 times the throughput. Extraction output semantics differ, so this is a speed comparison rather than an exact-output parity claim.
• The current branch passes 4,079 engine tests and 371 application tests.

PRs are welcome for engine performance and correctness, new input and output formats, PDF features, GUI integration, color correction tools, tests, documentation, and localization. Draft PRs are welcome too. If an idea needs a major dependency or changes a core architecture boundary, please start a discussion first.

Please target dev/1.9-overkill, keep each PR focused, and explain what you tested. Difficult real-world PDFs and small reproducible samples are especially useful.

The contribution guide covers the build and test process. The performance notes explain the published rendering measurements and their limits.

1.9 is still an active development build, but the engine is capable enough now that contributors can build meaningful features on top of it.