feat(types): DType carries its KClass witness; dtype-first storage constructors and loaders (SKEEP-003 P0, S0.2a)

[michalharakal]

Summary

SKEEP-003 slice S0.2a (milestone M0 #1001, decision #13 — merge LogicalDType into one sealed DType): DType carries its own witness, and every storage descriptor / loader can be built from a DType instead of a LogicalDType. Purely additive; LogicalDType is untouched (its deprecation is the separate slice #1014).

• sk.ainet.lang.types.DType: witness: KClass<out DType> (each of the 14 objects narrows to its own class, e.g. FP32.witness: KClass<FP32>), isSigned (false only for UInt*), sizeInBytes, companion entries (storage-layer order, index-aligned with LogicalDType.entries), fromWitness(kclass) / fromWitnessOrNull(kclass) (identity-keyed map — no name-based reflection, JS/Wasm-safe). fromWitness(tensor.dtype) is how M0's Format slice turns a Tensor.dtype into a DType.
• Additive dtype-first constructors/overloads (primary constructors unchanged): TensorStorage(shape, dtype, encoding, buffer, …), TensorStorageFactory.fromRawBytes / fromRawBytesOwned / fileBacked(… dtype: DType …), PackedBlockStorage.toTensorStorage(dtype, …); toTensorData dispatches on storage.dtype with identical semantics.
• Internal call sites moved to DType: TensorStorageFactory.fromFloatArray/fromIntArray, DefaultKvCacheStore, TurboQuantKvCacheStore, StreamingGGUFReader (ggmlTypeToDType; quantized → FP32, Opaque fallback kept), StreamingSafeTensorsReader (BOOL → UInt8, UNKNOWN → Int8 kept).
• Tests: DTypeWitnessTest (entries/order, witness identity, fromWitness inverse + rejection, signedness/width vs the storage enum, enum-like when), dtype twins in TensorStorageContractTest, StorageIntegrationTest asserts storage.dtype === FP32 for F32 and Q8_0 GGUF tensors.
• BCV: lang-core jvm dump regenerated (additions only).

Test plan

Full local gate (scripts/pr-gate.sh, JDK 25) + --golden; results in the first comment.

Closes #1007

🤖 Generated with Claude Code

[michalharakal]

Local gate scripts/pr-gate.sh (JDK 25) on ede2228:

=== pr-gate: JVM tests ===                                      BUILD SUCCESSFUL in 6m 32s
=== pr-gate: apiCheck ===                                       BUILD SUCCESSFUL in 1m 14s
=== pr-gate: verifyNpmPins jsTest wasmJsTest wasmWasiTest ===   BUILD SUCCESSFUL in 2m 39s
=== pr-gate: linuxX64Test ===                                   BUILD SUCCESSFUL in 1m 29s
=== pr-gate: assemble ===                                       BUILD SUCCESSFUL in 2m 9s
=== pr-gate: :skainet-test:skainet-test-java:test ===           BUILD SUCCESSFUL in 21s
pr-gate: all legs passed.

Targeted: lang-core sk.ainet.lang.types.* + sk.ainet.lang.tensor.storage.* 256/256, io-gguf + io-safetensors jvmTest green (497 tests total in the targeted run). Note on the class-init cycle (why the companion collections are lazy) is in the commit message and KDoc.

[github-actions]

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