[SDK: Python] Add Vehicles endpoints/interface

[infinityplusone]

Changes

• Add Vehicles endpoints to the Python SDK:
  • list_vehicles
  • get_vehicle
  • list_vehicle_awardees
• Add IDV endpoints to the Python SDK:
  • list_idvs
  • get_idv
  • list_idv_awards
  • list_idv_child_idvs
  • list_idv_transactions
  • get_idv_summary
  • list_idv_summary_awards
• Expand shaping support (explicit schemas + ShapeConfig) so common IDV expansions validate/materialize cleanly.
• Update docs + changelog.

Why

• Bring Python SDK endpoint coverage up to parity for Vehicles. Closes makegov/tango#1328.
• While here, wire the IDV endpoints since Vehicles are tightly coupled to IDVs in real usage.

Testing

• uv run pytest

Closes makegov/tango#1328

[vdavez]

One meta note: when writing tests, we should be using cassettes / real data instead of mocked data, especially for integration / smoke tests. It's just too easy for LLMs to guess at the shape of the data instead of actually using the data.

I'll handle the changes here, but this is something to watch out for going forward....