add 7 and 9 DOF to segreg

[m-reuter]

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[Copilot]

Pull request overview

Adds 7-DoF (similarity) and 9-DoF (rigid + anisotropic scale, no shear) transform models to segreg, extending centroid-based registration beyond rigid/affine while updating docs/CLI and adding solver + integration tests.

Changes:

• Implement find_similarity and find_rigid_anisotropic_scale solvers and route them via register_points(dof=7|9).
• Extend segreg() and the segreg CLI to accept DoF {6,7,9,12} and update defaults/docs accordingly.
• Add unit/integration tests for the new solvers and segreg() DoF modes; update README.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
neuroreg/segreg/points.py	Adds similarity + anisotropic no-shear solvers and DoF dispatch.
neuroreg/segreg/register.py	Expands segreg() DoF support and updates min-label defaults/docs.
neuroreg/cli/segreg.py	Updates CLI --dof choices and help text to include 7/9.
tests/test_segreg.py	Adds tests covering DoF 7/9 in both point solvers and segreg().
README.md	Documents new DoF support and updates the support table.
neuroreg/segreg/{__init__.py,atlas.py,centroids.py,io.py,labels.py}	Docstring/description updates to reflect expanded functionality.

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