WebAssembly bulk memory: execute memory operations and passive data lifecycle

Parent: #272 Depends on: #276 Roadmap: #263, #142, #134

Implement failure-atomic bulk memory execution and passive data segment state.

Acceptance:

• Instantiate active data segments failure-atomically and retain passive data per instance.
• Execute memory.init, data.drop, memory.copy, and memory.fill with exact unsigned bounds and trap ordering.
• Preserve memmove overlap semantics and make zero-length boundary cases spec-exact.
• Preserve dropped-segment behavior across repeated calls, traps, and imported memories.
• Add focused executor and JavaScript API coverage.

Completed in d5eef86a. Active data segments remain failure-atomic; passive data is per-instance and droppable; memory.init/data.drop/copy/fill implement unsigned preflight, exact zero-length boundaries, memmove overlap, dropped reuse traps, and imported/public API behavior. The executor and API filters are green, and the combined Wasm checkpoint is 159/159 with zero skips/failures/leaks.