Export harnesses cast external parameters to BufferHandle.Owned and crash on SKaiNET 0.53.0 (BufferHandle.Floats)

[michalharakal]

Symptom

FunctionGemmaExportDumpTest.exportAll_emitsContractShapesAndManifest and FunctionGemmaVmfbParityTest.vmfbTwoGraphKvLoopMatchesOracle fail on develop:

java.lang.ClassCastException: class sk.ainet.lang.tensor.storage.BufferHandle$Floats cannot be cast to class sk.ainet.lang.tensor.storage.BufferHandle$Owned
    at sk.ainet.models.functiongemma.FunctionGemmaExportHarness.writeSafetensors(FunctionGemmaExportHarness.kt:471)

Cause

Since SKaiNET 0.53.0 (SKaiNET#1247) the engine's ConstantMaterialization hands external parameters over as whatever BufferHandle the source data has — BufferHandle.Floats for FloatArray-backed constants, Owned for byte-backed ones — and provides DefaultBufferResolver / BufferAccessor.readAllBytes() to read any of them. Gemma3nExportHarness was updated to the resolver; these still hard-cast to BufferHandle.Owned:

• llm-inference/functiongemma/.../FunctionGemmaExportHarness.kt (writeSafetensors, writeSafetensorsInt8)
• llm-inference/smollm2/.../SmolLm2ExportHarness.kt
• llm-inference/whisper/src/jvmTest/.../WhisperExportHarness.kt (bytesOf, irpa storage segment — Owned/Borrowed only)
• llm-inference/gemma/src/jvmTest/.../RealGemmaBakeIrpaTest.kt, llm-inference/llama/src/jvmTest/.../RealSmolLm2BakeIrpaTest.kt

Fix

Read every external parameter through DefaultBufferResolver().resolve(handle).use { it.readAllBytes() } (little-endian f32 bytes regardless of handle kind) at all five sites. No behaviour change for Owned handles; the bf16 / int8 conversions keep their exact arithmetic.

Also on develop: the API dumps of bert, gemma, gemma3n, gemma-iree and kgemma have drifted from the code (apiCheck red); refreshed in the same PR.

[michalharakal]

Duplicate of #405 (filed independently before I found it) — fixed in #421 for the immediate crash; #414/#405 supersedes that fix in FunctionGemmaExportHarness.kt with a more complete chunked-streaming implementation. See the merge-conflict resolution on the functiongemma-export-floats-cast branch.