support Z'=1/3, 1/6

[KenHino]

Fix molecular placement on special Wyckoff positions of trigonal/hexagonal groups

Summary

pyxtal_molecule.get_orientations_in_wp returns no orientation for any special Wyckoff position of a trigonal or hexagonal space group (143–194), whatever the molecule's point group.
As a result, from_random cannot place a molecule on such a site and raises Symm_CompatibilityError, e.g. benzene (D6h) on the three-fold axis (6c) or the -3 site (3a) of R-3:

from pyxtal import pyxtal
c = pyxtal(molecular=True)
c.from_random(3, 148, ["Benzene"], [6], sites=[["6c"]])
# pyxtal.msg.Symm_CompatibilityError: Molecular symmetry is compatible with WP site

and Tris{2-[(2,6-dimethylphenyl)amino]ethyl}amine.

General positions and the inversion sites of the same groups are unaffected, which is why existing tests did not catch this.

Cause

get_orientations_in_wp and is_compatible_symmetry compare the site symmetry from Wyckoff_position.get_site_symm_wo_translation() against the molecule's Cartesian point-group operations.
That method returns the stored operations in fractional coordinates.
For hexagonal axes a 3-fold rotation is (-y, x-y, z), i.e. [[0,-1,0],[1,-1,0],[0,0,1]], which is not orthogonal.
OperationAnalyzer then cannot identify it as a rotation (type general, no axis), and PointGroupAnalyzer.is_valid_op applies it to Cartesian coordinates, which distorts the molecule, so every candidate orientation is rejected.

Changes

• Wyckoff_position.get_site_symm_wo_translation gains space: Literal["fractional", "euclidean"] = "fractional". "euclidean" uses get_site_symm_ops(), which differs from the stored operations only when self.euclidean is set.
• get_orientations_in_wp and is_compatible_symmetry request space="euclidean".
• The default stays "fractional", because is_pure_translation compares the result with the fractional generators and must keep doing so. Behaviour for groups 1–142 and 195–230 is unchanged.