Function openStreamedIfcModel

Open an IFC model from a streamed source with a fixed-memory parse (the release-facing Phase B API; composes M0/M1a/M7):

• the index builds through a moving window over source — the source is never resident in the JS heap, and the index is columnar from birth (no per-record object phase);
• the model reads source bytes on demand through a windowed LRU provider over store (ensureResidentByLocalID/ByExpressID page ranges in before synchronous reads — see DemandResidencyPump for the demand orchestration).

The typical browser wiring: a worker streams the network body through to OPFS while feeding the same bytes to source; store reads back from OPFS. source.byteLength and store.byteLength must agree.