Regenerate the reader from structure_schema.yml #1

src/topology.ts was written against an early, uncommitted exporter and is now wrong
against structure_schema.yml. It expects a wing_sections block that is called
stations, declares tethers / winches / pulleys as required when the schema makes
them optional, and knows nothing about bodies, elastic_joints or timoshenko_joints.

• Generate the types from the schema rather than hand-writing them. A hand-written
  mirror of a schema is a second definition of the same thing and drifts on the first
  change. Vendor the schema at a pinned version.
• Replace the SUPPORTED_SCHEMA = "structure_schema.yml" handshake — that is a
  filename, not a version, so both sides compare the same literal and every future
  breaking change passes the check. The rule the schema states is: refuse an unknown
  major awesIO_version, warn on an unknown minor.
• Validate connectivity_sha and delete the two n_points branches in decodeRun; the
  hash is the strong form of the same test.
• Treat an absent optional block as an empty one.

Done when the reader is generated, the version rule is implemented, and a run
recorded against a different structure is refused by hash rather than by point count.

Depends on the schema, which exists. Nothing else in this repo should be done before it. Tracked by OpenSourceAWE/symawe.com#1.