fix: preserve observation-major Harmony output

[mvanhorn]

Update _harmony in snapatac2/preprocessing/_harmony.py to normalize Z_corr against the input observation count: keep an observation-major result unchanged and transpose a component-major result for compatibility with older harmonypy releases. snap.pp.harmony currently transposes harmonypy's Z_corr result unconditionally before its public wrapper stores the matrix in .obsm.

Verify observation-major Z_corr is returned unchanged and can be written by harmony(..., inplace=True) to an AnnData .obsm entry with shape (n_obs, n_components); Verify legacy component-major Z_corr is transposed to the same observation-major shape, including the inplace=False return path.

Closes #465

[kaizhang]

Thanks! I think the tests can be removed for such a small change.