Introduces a plugin capability that runs Python at the seams of Print::process(),
letting a plugin read and rewrite slicing state as it is computed.
- New slicing_pipeline_plugin config option; selected plugin refs are serialized
into the print manifest.
- Print gains an injectable hook fired at each pipeline step (posSlice,
posPerimeters, posInfill, ...). It is a no-op when unset, fires only on genuine
(re)computation, and never on the use-cache path.
- orca.slicing submodule: SlicingPipelineCapabilityBase plus a trampoline and a
Step enum. Capabilities read the live graph through zero-copy int64 numpy views
(contour/holes geometry with unscaled coordinates, flattened toolpath data) and
edit it through 2D-geometry mutators with cache-invariant refresh.
- GUI dispatcher runs capabilities during slicing under the GIL, turns plugin
errors into slicing errors, honors cancellation, and adds the plugin picker.
- Ships the InsetEverySlice sample plugin and binding/hook tests.
