Nodejs Heap Metrics

Add per-worker Node.js heap metrics to the OTel meter — nodejs.memory.heap.used, nodejs.memory.heap.total, nodejs.memory.heap.limit, nodejs.memory.external, nodejs.memory.array_buffers, nodejs.memory.rss. Host-metrics only publishes RSS, which overstates V8 heap by the external + native footprint; these give direct heap visibility per cluster worker so NODE_MAX_OLD_SPACE_SIZE can be sized against observed heap peaks rather than RSS.