Return QuTiP backend results as OQD datastores

[glasses666]

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Closes #44.

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Feature: updates the QuTiP backend result API to return an oqd_dataschema.Datastore.

• What is the current behavior? (You can also link to an open issue here)

QutipBackend.run(...) currently returns an ad hoc dict containing QuTiP runtime objects (final_state, states, tspan, frame, hilbert_space), which cannot be saved through the shared OQD dataschema HDF5 path.

• What is the new behavior (if this is a feature change)?

QutipBackend.run(...) now returns a Datastore with one "emulation" group containing:

• tspan: float timeline dataset
• states: complex ket or density-matrix trajectory dataset
• final_state: complex final ket or density matrix dataset
• scalar attrs for backend, solver, timestep, Hilbert-space sizes, fock cutoff, and frame presence/type

The QuTiP VM execution path is unchanged; the old VM result is wrapped after execution. The QuTiP reference docs now show the new Datastore usage and HDF5 dump path.

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

Yes. Code using result["tspan"] / result["states"] now needs to access the datastore group, for example result["emulation"].tspan.data and result["emulation"].states.data. This matches the requested issue behavior.

• Other information:

Depends on OpenQuantumDesign/oqd-dataschema#12, which adds TrICalEmulatorDataGroup. To keep this PR testable before that schema PR lands, the temporary uv source points at glasses666/oqd-dataschema:codex/unitaryhack-44-trical-group. After #12 is merged, I can update this PR to point back at OpenQuantumDesign/oqd-dataschema and relock.

AI-assisted with OpenAI Codex; the diff was reviewed and locally verified before submission.

Validation run locally:

uv run --with-editable ../oqd-dataschema --extra tests pytest tests/ -q
3 passed, 2 xfailed

uv run --with-editable ../oqd-dataschema ruff check src tests
All checks passed!

git diff --check
passed

[benjimaclellan]

@glasses666 Thanks for the PR, this looks good and meets all the requirements for #44. The branch for the oqd-dataschema in pyproject.toml will need to change once everything has been merged, but that is an easy tweak.