Story: Migrate legacy EWKT parser tests and document EWKT decoding #14

Goal

Complete the migration from longitude-one/wkt-parser by recovering its existing unit tests and adapting them to the new spatial-decoder architecture.

The migrated suite must remain identifiable as legacy compatibility coverage while new tests remain the authoritative coverage for the current decoder behavior. Public documentation must describe the resulting EWKT decoding capabilities and limitations.

Acceptance criteria

• Existing wkt-parser unit tests are identified and reviewed.
• Compatible legacy tests are migrated under tests/Legacy/EwktParser/.
• Migrated tests use the public spatial-decoder API.
• Original test scenarios remain identifiable for traceability.
• Legacy expectations conflicting with the current specification are not preserved silently.
• Any intentionally modified or excluded legacy behavior is documented.
• Migrated tests run as part of the standard PHPUnit and CI suites.
• Documentation describes supported EWKT geometry types and dimensions.
• Documentation describes EMPTY handling and unsupported representations.
• Documentation provides usage examples through the public Decoder API.
• The standard test and quality suites pass.

Out of scope

• Changes to the public API of longitude-one/wkt-parser.
• Deprecation or archival of longitude-one/wkt-parser.
• EWKB or GeoJSON documentation.
• WKT support.