Epic: Support mutable and immutable spatial objects

Context

spatial-types currently exposes immutable spatial objects. Some consumers need to edit coordinates and aggregate membership progressively while retaining object identity.

The completed #36 provides partially null point ordinates. This Epic preserves that representation freedom in both object variants.

Objective

Allow consumers to choose a mutable or immutable representation for every currently supported spatial type and coordinate dimension, with explicit contracts for coordinates, family, spatial reference and aggregate components.

Scope

• First rename existing concrete spatial classes with the Immutable suffix and make them final, preserving immutable behavior and their dimension/family namespaces. Remove former names without aliases or deprecation; the library has never been in production.
• Introduce mutable classes without a suffix directly under their dimension namespace, alongside Geometry and Geography.
• Share read-only interfaces and suitable abstract bases without mutable classes extending concrete immutable classes. Separate ImmutableInterface copy contracts from MutableInterface mutation contracts.
• Support in-place editing of available ordinates, declared family, declared spatial reference and aggregate membership. The final mutable-constructor parameter is SpatialModelEnum, defaulting to SpatialModelEnum::GEOMETRY.
• Provide type-specific editing operations, including circular-string origin, arc append and arc replacement.
• Reserve with… methods exclusively for immutable variants and set…/add…/remove… methods for mutable variants. Immutable aggregates reject mutable spatial components without implicit conversion.
• Adapt factories and document ownership, propagation and consumer-facing contracts.

Each instance retains its spatial type and coordinate dimension, with no dimension setter. MutableSpatialInterface exposes setters for declared SRID/reference and spatial mode (Geometry/Geography). Family and declared-reference changes never recalculate coordinates. Dimension conversion and coordinate transformation belong to spatial-transformer.

Geometric validity remains an explicit spatial-validator concern. Incomplete coordinates, including Point(0, null), remain representable. No mutation or copy path may reintroduce geometric validation.

Stories

• Story: Preserve immutable types under explicit names and shared contracts #39 Preserve immutable types under explicit names and shared contracts
• Story: Edit point coordinates and declared spatial context in place #40 Edit point coordinates and declared spatial context in place
• Story: Edit line strings and circular strings in place #41 Edit line strings and circular strings in place
• Story: Edit compound curves in place #42 Edit compound curves in place
• Story: Edit polygons and triangles in place #43 Edit polygons and triangles in place
• Story: Edit polyhedral surfaces in place #44 Edit polyhedral surfaces in place
• Story: Edit multi-objects and spatial collections in place #45 Edit multi-objects and spatial collections in place
• Story: Create spatial types through public factories with a shared mutability mode #46 Create both spatial representations through factories and document their use

This list may evolve during refinement.

Completion Criteria

• All Stories required to achieve the objective are complete.
• Both representations are available for the supported types and dimensions within the defined scope.
• No unresolved work required by the scope remains.