QgdScan::Mrm::event_id decoded and tested, then discarded before reaching output

[Nathan-D-R]

Found during the 2026-07-24 cross-repo parity sweep.

crates/openszraw/src/raw/qgd.rs:24 parses and unit-tests event_id for MRM scans, but reader.rs:270 destructures it away (qgd::QgdScan::Mrm { transitions, .. }) - none of the per-transition SpectrumRecords emitted from one scan carry any indication of which acquisition event they came from.

Same shape of gap as OpenSZRaw's cycle_index/QTOF finding (a decoded grouping key never reaching the schema layer), independently occurring in a different vendor variant's code path.

Effort: small.