Texture uniform odf

[bnmajor]

Overview

Adds UniformODF, a constant orientation distribution function representing completely random (isotropic) texture. The ODF evaluates to a constant 1 MRD (multiples of a random distribution) for every orientation - the standard reference density for texture analysis on SO(3).

New API (additive only — no existing signatures changed)

• hexrd.phase_transition.texture.UniformODF/hexrd.phase_transition.texture.uniform_odf:
  • .eval(orientations: np.ndarray) -> float | np.ndarray - returns a scalar 1.0 for a single (3, 3) matrix and an array of ones for any input whose shape ends in (3, 3); raises ValueError otherwise.

Tests added

• Package export, constant 1 MRD value, and MRD convention.
• Symmetry validation (valid + invalid crystal/sample)
• Evaluation: single orientation (scalar), batched (N, 3, 3) and multi-dimensional (2, 2, 3, 3) inputs, and invalid-shape handling.
• All orientations return equal values; value is 1 MRD across crystal symmetries.
• Guard the mirrored symmetry sets against drift from WPPF's SYMLIST

Who might need to know

• Anyone building texture/ODF functionality on hexrd.phase_transition.texture, since UniformODF establishes the ODF eval() interface contract.
• Maintainers of hexrd.powder.wppf.texture - UniformODF mirrors (to avoid depending on WPPF) SYMLIST, and a test will fail if the crystal symmetry list there changes.

Affected Workflows

No existing workflows change behavior - this is purely additive. New texture/ODF code can now use UniformODF as a random-texture reference. Nno change to existing public APIs, CLI, or file formats.

Documentation Changes

• No separate docs site/repo updates required; the public API is documented via docstrings

Other notes

• Symmetry is validated and stored but intentionally inert. The uniform ODF value is constant regardless of symmetry; the arguments exist to satisfy the common ODF interface planned for the upcoming UnimodalODF work.
• 'axial' sample symmetry was dropped. The sample set is restricted to {triclinic, monoclinic, orthorhombic} to match DeLaValleePoussinKernels supported sample symmetries. 'axial' has no current consumer.
• Symmetry labels are mirrored from hexrd.powder.wppf.texture.SYMLIST rather than imported, to keep the new texture package decoupled from WPPF. A regression test guards against drift. If depending on WPPF is acceptable this can be changed to import the labels and the regression test can be dropped.

Depends on #926