improve SpacingD output shape compute stability

[wyli]

for slightly different affine (atol < 1e-3) the shape output might be different

sum([1.49999991e+00 1.44128689e-04] * [237. 144.]) = sum([3.55499980e+02 2.07545313e-02]) = 355.52073414989167

sum([ 1.49999989e+00 -6.16167492e-10] * [237. 144.]) = sum([ 3.55499975e+02 -8.87281188e-08]) = 355.4999748785736

• increase the stability of affine inv
• check affine floating point types
• ensure same shape when there's only tiny difference in pixdim

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[myron]

Looks good. Thanks!

[wyli]

/build

[wyli]

/black

[wyli]

/build