build: restore conda-forge pyobjcryst and diffpy.cmistructure in requirements and CI before release #9

Problem

The new code relies on pyobjcryst features that are only on upstream main, such as ReflectionProfilePseudoVoigtTCH, added in diffpy/pyobjcryst#115. The latest conda-forge release, pyobjcryst 2026.1.0, doesn't have them. It also pins libobjcryst <2026.3.0, while upstream main needs libobjcryst >=2026.3.0.

As a temporary workaround, the PR tests compile pyobjcryst from source. diffpy.cmirietveld can't be released until this is reverted.

Proposed solution

After a pyobjcryst release with these features is on conda-forge and before cmirietveld is ever released:

In requirements/conda.txt, replace

libobjcryst>=2026.3.0
libboost-devel
libboost-python

with

pyobjcryst
diffpy.cmistructure

In .github/workflows/tests-on-pr.yml, replace

      headless: false
      run: |
        python -m pip install git+https://github.com/diffpy/pyobjcryst.git@d6a1279a26b9b1e6e303d103935b4469c5a62e41 --no-deps
        python -m pip install diffpy.cmistructure --no-deps

with

      headless: false