[Lane 2 · kotlin-core] ONNX importer — streaming tensor loading in OnnxModelReader #1407

Sub-issue of #1400 ([Feature]: ONNX importer — replace placeholder ops with real operations, stream tensors in OnnxModelReader).

Lane: 2 · Kotlin core
Skill needed: Kotlin; protobuf wire format basics.
Size: m (1–2 days)
Blocked by: nothing

What to do

1. Implement OnnxModelReader.loadTensor (skainet-io/skainet-io-onnx/src/commonMain/kotlin/sk/ainet/io/onnx/OnnxModelReader.kt) and populate tensors / metadata by recording initializer offsets with ProtobufWireReader instead of materialising everything.
2. Use the GGUF streaming reader (StreamingGgufParametersLoader) as the pattern for lazy loading.
3. Remove the file's line from config/stub-allowlist.txt and run ./gradlew :skainet-io:skainet-io-onnx:jvmTest checkUnmarkedStubs.

Acceptance

• Initializers of a small test model load lazily with correct values
• checkUnmarkedStubs passes without the allowlist entry
• Result reported back on the parent issue

Notes

If something here turns out to be wrong or much bigger than the size label, comment on this issue or open a specific bug instead of blocking the parent.

Coverage matrix: docs/modules/ROOT/pages/reference/ops-status-matrix.adoc · How lanes work: Issue taxonomy