refactor!: make PlaneGeometry fields private

[FreezyLemon]

These should not have been public in the first place. This makes invalid state between geometry and data impossible (fixing any problems related to #61) and results in a nicer API overall.

Basically: Plane and AlignedData have safety invariants that depend on the state of PlaneGeometry when Plane::new is called. By both validating the geometry in its constructor and making it fully immutable, we ensure that the invariants are always fulfilled.

This also means we can remove the re-validation of geometry (part of #74) from Plane::new.

Changes:

• add getters
• make getters return zeroable scalars over NonZero. With #[inline] this should elide unnecessary width != 0 checks downstream while making the API simpler (plane.width().get() -> plane.width())
• move data_origin from Plane to geometry, not something downstream needs without padding awareness (-> -F padding_api)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.40%. Comparing base (59bc0dc) to head (d7140e4).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #75      +/-   ##
==========================================
- Coverage   99.40%   99.40%   -0.01%     
==========================================
  Files           7        7              
  Lines         668      667       -1     
==========================================
- Hits          664      663       -1     
  Misses          4        4              

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