Fix checked native barcode crop bounds

[Szer]

Horizontal barcode crops retained the image's row stride but supplied a span shorter than ZXingCpp's checked ImageView requires. Valid images therefore threw an out-of-bounds exception and prematurely abandoned the remaining native crops.

Supply the full required stride and add one trailing row of managed buffer padding so bottom-edge crops also remain within bounds. This retains bounded spans and scoped pinning, with no unsafe code or per-crop pixel copies. Extract the native reader so behavioral regression tests can observe failures otherwise hidden by managed fallback.

Validation:

• Reproduced before fixing: three blank-image cases failed with the production exception; both affected production photos and four existing fixtures also reproduced it.
• Offline OCR suite: 34 tests pass, including blank-image and difficult-fixture regressions.
• Saved 2,201-image corpus: zero native exceptions and unchanged barcode outputs.
• Both production photos now complete native search without exceptions; their final recognition results remain unchanged.

Coupon build and deploy tests use Ubuntu 24.04 ARM, matching the production image’s Noble base. Ubuntu 22.04 cannot load the packaged native library because it requires GLIBC_2.38; direct reader regressions exposed this previously hidden fallback. Other bots retain their existing runner default.