add multireference quantum chemistry

[EBB2675]

Purpose

Adds multireference quantum-chemistry related extensions to the schema.
Since these methods are only well defined in the presence of a defined active orbital space, this PR also introduces two utility modules demonstrating how MolecularOrbitals can be integrated and referenced at the schema level.
This paves the way for future GUI implementations to include a visualization for active molecular orbitals.

Scope

• Adds a minimal ActiveSpace schema section to describe the active orbital and electron subspace used by multireference methods. This base is designed to be used by all downstream methods as a subsection.
• Adds a flexible multireference method layer, BaseMultireferenceMethod which includes share method parameters.
• Adds three main classes extending the base, MultireferenceSCF, MultireferenceCI, MultireferencePT, to further group the methods.
• Adds utilities for molecular-orbital artifacts: utils/mo_cube.py, utils/mo_trexio.py and their corresponding unit tests.

Out of scope (What is explicitly not included (to avoid scope creep)?)

• Advanced numerical setting knobs are out of scope, and will be added in the near future to numerical_settings.py
• These methods are almost always used as workflows, e.g.,

DFT + CASSCF  + CASCI  + CASPT2 (4 sequential runs to simulate one X-ray emission spectra)
HF  + DMRFSCF + DMRGCI + NEVPT2 (4 sequential runs to simulate one absorption spectra)

The current PR only involves the method descriptions for each step.

Status

Select one

• Draft / In progress (not ready for full review)
• Ready for review
• Blocked (explain below)

Dependencies / Blockers

List anything that may block progress or review

• None.
• Related PRs:
• Open design questions:
• External dependencies (people, decisions, data, releases):

Testing / Validation

How was this change validated?

• Unit tests
• Integration tests
• Manual testing (brief description):
  I have added a set of example uploads to nomad-simulation-examples, to showcase the parsed archives.

Linked Issues / Context

Use GitHub keywords where applicable.

• Fixes #
• Related to Add schema support for multireference quantum chemistry #308
• Follow-up issues (if known):

Context & Links

For more context, I have created a summary file in simple English to navigate reviewers better:

Reviewer Notes

[coveralls]

Pull Request Test Coverage Report for Build 20433944122

Details

• 166 of 179 (92.74%) changed or added relevant lines in 7 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 82.237%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/nomad_simulations/schema_packages/model_method.py	30	32	93.75%
src/nomad_simulations/utils/mo_cube.py	34	36	94.44%
src/nomad_simulations/utils/mo_trexio.py	36	45	80.0%

Totals
Change from base Build 20363295729:	0.2%
Covered Lines:	7324
Relevant Lines:	8906

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💛 - Coveralls

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 9 comments.

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[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Comments suppressed due to low confidence (1)

src/nomad_simulations/utils/mo_cube.py:13

• Import of 'Optional' is not used.

from typing import Optional

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