Story: Decode WKT collection geometries #11

Goal

Add WKT decoding support for MULTIPOINT and GEOMETRYCOLLECTION geometries.

The decoder must support nested and heterogeneous geometry structures where permitted, recursively decode their components, and construct the corresponding immutable spatial objects without losing spatial information.

Acceptance criteria

• MULTIPOINT is decoded into the corresponding spatial object.
• Supported MULTIPOINT WKT representations are correctly handled.
• GEOMETRYCOLLECTION is decoded into the corresponding spatial object.
• Geometry collections may contain supported heterogeneous geometry types.
• Nested geometry collections are correctly decoded.
• XY, XYZ, XYM and XYZM representations are supported where applicable.
• EMPTY representations are supported.
• Invalid or inconsistent collection structures are explicitly rejected.
• Unit tests cover supported collections, nesting, dimensions, EMPTY, and invalid representations.
• The standard test and quality suites pass.

Out of scope

• Geometry types not implemented by the spatial object model.
• EWKT and SRID-prefixed representations.
• Implicit conversion of collection members.
• Coordinate reprojection.