Add AnalogEmulatorDataGroup for analog emulator output

[CodeMaverick2]

Summary

Adds AnalogEmulatorDataGroup - the shared HDF5 schema for classical analog emulator runs (unitaryHACK / oqd-analog-emulator #9).

Datasets: times, metrics (2D + metric_labels in attrs as JSON), state (2D trajectory), optional measurements.

Group attrs: run metadata (backend, dt, fock_cutoff, n_shots, etc.).

Why separate PR

Emulator backends should not define their own on-disk format. This group is registered in GroupRegistry and exported from oqd_dataschema.

Test plan

• pytest tests/test_analog_emulator_group.py — registration + HDF5 round-trip
• Full suite: 147 passed, 57 xfailed (unchanged from main)

Merge order

Merge this before oqd-analog-emulator #10.

[CodeMaverick2]

@benjimaclellan Would love to know your thoughts on PR

[benjimaclellan]

Thanks for the work! Data structure looks clean and everything seems good. I'll leave comments over in the analog-emulator repo for the rest of the issue.

[CodeMaverick2]

@benjimaclellan ready for merge whenever you are.

Merge order:

1. oqd-dataschema #11 first
2. Then oqd-analog-emulator #10

Let me know if anything else needs tweaking.