Story: Decode WKT surface geometries #10

Goal

Add WKT decoding support for POLYGON and MULTIPOLYGON geometries.

The decoder must correctly parse rings and nested polygon structures, preserve coordinate dimensions and ordering, and construct the corresponding immutable spatial objects while enforcing the applicable structural constraints.

Acceptance criteria

• POLYGON is decoded into the corresponding spatial object.
• MULTIPOLYGON is decoded into the corresponding spatial object.
• Exterior and interior rings are correctly decoded and preserved.
• XY, XYZ, XYM and XYZM coordinates are supported.
• EMPTY representations are supported.
• Coordinate values, ordering and dimensions are preserved.
• Invalid or structurally inconsistent representations are explicitly rejected.
• Unit tests cover supported types, dimensions, rings, EMPTY, and invalid representations.
• The standard test and quality suites pass.

Out of scope

• Point, curve and collection geometry types.
• EWKT and SRID-prefixed representations.
• Geometry repair or normalization.
• Coordinate reprojection.