feat(imaging): add pure-Rust JPEG 2000 backend (#109)

ci/ci-coverage.json

@@ -12,6 +12,7 @@
     "compatibility-parity",
     "minimal-features",
     "jpeg2000",
+    "rust-j2k",
     "skia-binary",
     "program-offline-smoke",
     "clippy",
@@ -66,10 +67,10 @@
     },
     {
       "workflow": "jpeg2000.yml",
-      "responsibility": "Optional OpenJPEG/JPEG 2000 feature build and tests",
+      "responsibility": "Independent OpenJPEG and pure-Rust JPEG 2000 feature builds, tests, and interoperability",
       "destination": "required",
-      "checks": ["jpeg2000"],
-      "rationale": "The optional native codec is tested independently with an exact cached OpenJPEG 2.5.4 identity."
+      "checks": ["jpeg2000", "rust-j2k"],
+      "rationale": "The optional native codec is tested with exact OpenJPEG 2.5.4 and the pure-Rust codec is tested independently and together with it."
     },
     {
       "workflow": "performance.yml",
@@ -89,7 +90,7 @@
       "workflow": "release-matrix.yml",
       "responsibility": "MSRV, default, minimal, features, release profiles, and portable cross-target checks",
       "destination": "split",
-      "checks": ["minimal-features", "jpeg2000", "skia-binary", "msrv", "portable-cross-targets", "release-profile"],
+      "checks": ["minimal-features", "jpeg2000", "rust-j2k", "skia-binary", "msrv", "portable-cross-targets", "release-profile"],
       "rationale": "Fast feature isolation remains required; clean MSRV, cross-target, and release-profile builds run non-routinely."
     },
     {