BridgeJS: Optimize numeric array transfer with bulk TypedArray copy

[krodak]

Overview

Optimize numeric array transfer by using bulk TypedArray memory copy instead of element-by-element stack serialization. When a Swift function passes or receives a numeric array ([Int], [UInt8], [Float], [Double], etc.), BridgeJS now transfers the data as a single bulk operation. TypeScript types remain number[] / bigint[] — no user-facing API change.

This is a transparent performance optimization following the same pattern as bridgeJSStackPopAsOptional — a specialized ABI for numeric element types without changing the type contract. Non-numeric arrays ([String], [MyStruct], etc.) continue using the existing element-by-element stack protocol.

1. Swift → JS direction: Array.bridgeJSTypedArrayPush() calls withUnsafeBufferPointer to pass (ptr, count, kind) to a new swift_js_push_typed_array WASM import, which copies the bytes into a JS TypedArray. A pre-allocated for-loop then converts to number[] for the caller.

2. JS → Swift direction: [T].bridgeJSTypedArrayLiftParameter(sourceId, count) receives a retained TypedArray from JS, allocates via Array(unsafeUninitializedCapacity:), and calls back to JS via swift_js_init_typed_array_memory to bulk copy — the same retain-allocate-callback pattern used by string lowering.

3. Affected types: All integer types (Int8 through Int64, signed and unsigned), Float, Double, plus pointer-width Int/UInt. A new _BridgeJSTypedArrayElement protocol marks eligible types. BridgeType.isNumericScalar and typedArrayKind on the skeleton side route the codegen.

Benchmark results

Release build, 10K iterations × 5 runs:

Test	Before	After	Speedup
takeIntArray (1K, JS→Swift)	758 ms	13 ms	58×
takeDoubleArray (1K, JS→Swift)	791 ms	13 ms	61×
makeIntArray (1K, Swift→JS)	221 ms	18 ms	12×
makeIntArrayLarge (10K, Swift→JS)	2160 ms	146 ms	15×
roundtripIntArray (1K)	964 ms	29 ms	33×
takeStringArray (non-numeric)	23 ms	25 ms	unchanged