Finish the convex hull node: in-repo algorithm, robustness, and tests

Replaces the WIP node crate, which depended on a convex_hull crate that
only existed outside the repository, with a self-contained implementation:

- The curved hull algorithm lives in vector-types' algorithms module. It
  splits curves at inflections and cusps into curvature-monotone arcs,
  discovers the boundary structure from a sampled polygonal hull, refines
  every transition to an exact tangency with closed-form quartic
  tangent-through-point solves, then emits the boundary as cuts of the
  original segments joined by straight bridge lines.

- The node moves into vector-nodes alongside the other 'Vector: Modifier'
  nodes, ported to the List/attributes model. It accepts Graphic[] or
  Vector[], wraps every subpath (open or closed) and free-floating anchor
  point across all items, and outputs a single world-space hull path.

- The boolean-union pre-pass is dropped as unnecessary: the hull of all
  segments equals the hull of their union, and the polyline connector it
  relied on lost floating points and mishandled open paths.

node-graph/libraries/vector-types/src/vector/algorithms/mod.rs

@@ -1,5 +1,6 @@
 pub mod bezpath_algorithms;
 mod contants;
+pub mod convex_hull;
 pub mod intersection;
 pub mod merge_by_distance;
 pub mod offset_subpath;