Nexus: magnetization density estimator

[kayahans]

Add capability to define magnetizationdensity estimator in Nexus. Relevant nexus tests are also added.

What type(s) of changes does this code introduce?

• New feature

Does this introduce a breaking change?

• No

What systems has this change been tested on?

MacOS 15.3.1

Checklist

• Yes. This PR is up to date with current the current state of 'develop'
• No. Code added or changed in the PR has been clang-formatted
• Yes. This PR adds tests to cover any new code, or to catch a bug that is being fixed
• No. Documentation has been added (if appropriate)

[prckent]

Please add an example of using this to nexus/examples/qmcpack/rsqmc_misc/estimators/iron_ldaU_dmc.py . That example is the closest we have to documentation of what observables can be driven by NEXUS.

[prckent]

LGTM

Thanks Kayahan.

[prckent]

Test this please

[prckent]

Small updates likely needed:

957/1339 Test #2629: ntest_nexus_qmcpack_input ................................................................................***Failed    0.55 sec
Test name     : qmcpack_input
Test sublabel : test_magnetization_density
Test exception: "AssertionError: Missing or incorrect pattern: <parameter name="integrator" > simpson </parameter>"
Test backtrace:
  File "/scratch/ci/actions-runner-1/_work/qmcpack/qmcpack/nexus/bin/nxs-test", line 478, in run
    self.operation()
  File "/scratch/ci/actions-runner-1/_work/qmcpack/qmcpack/nexus/bin/nxs-test", line 1298, in qmcpack_input
    nunit_all()
  File "/scratch/ci/actions-runner-1/_work/qmcpack/qmcpack/nexus/bin/nxs-test", line 362, in nunit_all
    run_external_unit_test(test_name,unit_test)
  File "/scratch/ci/actions-runner-1/_work/qmcpack/qmcpack/nexus/bin/nxs-test", line 388, in run_external_unit_test
    unit_test()
  File "/scratch/ci/actions-runner-1/_work/qmcpack/qmcpack/nexus/tests/unit/test_qmcpack_input.py", line 2021, in test_magnetization_density
    assert pattern_in_text(pattern, text), f"Missing or incorrect pattern: {pattern}"

[kayahans]

@prckent sorry I realized that I had changed "simpson" to simpsons in the last commit, but realized that didn't make the change everywhere. The test now passes again:

./nxs-test -R qmcpack_input

 1/1 qmcpack_input...........................   Passed  0.38 sec

100% tests passed, 0 tests failed out of 1

Total test time = 0.38 sec

[ye-luo]

Test this please